diff --git a/docs/pip_sphinxext.py b/docs/pip_sphinxext.py
index a0e69c6e4c2..3336bd50993 100644
--- a/docs/pip_sphinxext.py
+++ b/docs/pip_sphinxext.py
@@ -42,15 +42,16 @@ def run(self):
 class PipOptions(rst.Directive):
 
     def _format_option(self, option, cmd_name=None):
-        if cmd_name:
-            bookmark_line = ".. _`%s_%s`:" % (cmd_name, option._long_opts[0])
-        else:
-            bookmark_line = ".. _`%s`:" % option._long_opts[0]
+        bookmark_line = (
+            ".. _`{cmd_name}_{option.long_opts[0]}`:"
+            if cmd_name else
+            ".. _`{option.long_opts[0]}`:"
+        ).format(**locals())
         line = ".. option:: "
         if option._short_opts:
             line += option._short_opts[0]
         if option._short_opts and option._long_opts:
-            line += ", %s" % option._long_opts[0]
+            line += ", " + option._long_opts[0]
         elif option._long_opts:
             line += option._long_opts[0]
         if option.takes_value():
@@ -60,7 +61,7 @@ def _format_option(self, option, cmd_name=None):
         opt_help = option.help.replace('%default', str(option.default))
         # fix paths with sys.prefix
         opt_help = opt_help.replace(sys.prefix, "<sys.prefix>")
-        return [bookmark_line, "", line, "", "    %s" % opt_help, ""]
+        return [bookmark_line, "", line, "", "    " + opt_help, ""]
 
     def _format_options(self, options, cmd_name=None):
         for option in options:
diff --git a/src/pip/_internal/cli/main_parser.py b/src/pip/_internal/cli/main_parser.py
index 4871956c9de..08c82c1f711 100644
--- a/src/pip/_internal/cli/main_parser.py
+++ b/src/pip/_internal/cli/main_parser.py
@@ -48,7 +48,7 @@ def create_main_parser():
 
     # create command listing for description
     description = [''] + [
-        '%-27s %s' % (name, command_info.summary)
+        '{name:27} {command_info.summary}'.format(**locals())
         for name, command_info in commands_dict.items()
     ]
     parser.description = '\n'.join(description)
diff --git a/src/pip/_internal/cli/parser.py b/src/pip/_internal/cli/parser.py
index e799215bef1..04e00b72132 100644
--- a/src/pip/_internal/cli/parser.py
+++ b/src/pip/_internal/cli/parser.py
@@ -31,14 +31,14 @@ def __init__(self, *args, **kwargs):
         optparse.IndentedHelpFormatter.__init__(self, *args, **kwargs)
 
     def format_option_strings(self, option):
-        return self._format_option_strings(option, ' <%s>', ', ')
+        return self._format_option_strings(option)
 
     def _format_option_strings(self, option, mvarfmt=' <{}>', optsep=', '):
         """
         Return a comma-separated list of option strings and metavars.
 
         :param option:  tuple of (short opt, long opt), e.g: ('-f', '--format')
-        :param mvarfmt: metavar format string - evaluated as mvarfmt % metavar
+        :param mvarfmt: metavar format string
         :param optsep:  separator
         """
         opts = []
diff --git a/src/pip/_internal/cli/progress_bars.py b/src/pip/_internal/cli/progress_bars.py
index 7ed224790cf..94e753bd666 100644
--- a/src/pip/_internal/cli/progress_bars.py
+++ b/src/pip/_internal/cli/progress_bars.py
@@ -124,7 +124,7 @@ def update(self):
 
 class BlueEmojiBar(IncrementalBar):
 
-    suffix = "%(percent)d%%"
+    suffix = "{percent}%"
     bar_prefix = " "
     bar_suffix = " "
     phases = (u"\U0001F539", u"\U0001F537", u"\U0001F535")  # type: Any
@@ -203,8 +203,8 @@ class BaseDownloadProgressBar(WindowsMixin, InterruptibleMixin,
                               DownloadProgressMixin):
 
     file = sys.stdout
-    message = "%(percent)d%%"
-    suffix = "%(downloaded)s %(download_speed)s %(pretty_eta)s"
+    message = "{percent}%"
+    suffix = "{downloaded} {download_speed} {pretty_eta}"
 
 # NOTE: The "type: ignore" comments on the following classes are there to
 #       work around https://github.com/python/typing/issues/241
@@ -238,7 +238,7 @@ class DownloadProgressSpinner(WindowsMixin, InterruptibleMixin,
                               DownloadProgressMixin, Spinner):
 
     file = sys.stdout
-    suffix = "%(downloaded)s %(download_speed)s"
+    suffix = "{downloaded} {download_speed}"
 
     def next_phase(self):  # type: ignore
         if not hasattr(self, "_phaser"):
@@ -247,17 +247,10 @@ def next_phase(self):  # type: ignore
 
     def update(self):
         # type: () -> None
-        message = self.message % self
+        message = self.message.format(vars(self))
         phase = self.next_phase()
-        suffix = self.suffix % self
-        line = ''.join([
-            message,
-            " " if message else "",
-            phase,
-            " " if suffix else "",
-            suffix,
-        ])
-
+        suffix = self.suffix.format(vars(self))
+        line = " ".join(filter(None, (message, phase, suffix)))
         self.writeln(line)
 
 
diff --git a/src/pip/_internal/cli/req_command.py b/src/pip/_internal/cli/req_command.py
index 21770df62e2..db7b3138a58 100644
--- a/src/pip/_internal/cli/req_command.py
+++ b/src/pip/_internal/cli/req_command.py
@@ -342,13 +342,13 @@ def get_requirements(
             opts = {'name': self.name}
             if options.find_links:
                 raise CommandError(
-                    'You must give at least one requirement to %(name)s '
-                    '(maybe you meant "pip %(name)s %(links)s"?)' %
-                    dict(opts, links=' '.join(options.find_links)))
+                    'You must give at least one requirement to {name} '
+                    '(maybe you meant "pip {name} {links}"?)'.format(
+                    **dict(opts, links=' '.join(options.find_links))))
             else:
                 raise CommandError(
-                    'You must give at least one requirement to %(name)s '
-                    '(see "pip help %(name)s")' % opts)
+                    'You must give at least one requirement to {name} '
+                    '(see "pip help {name}")'.format(**opts))
 
         return requirements
 
diff --git a/src/pip/_internal/cli/spinners.py b/src/pip/_internal/cli/spinners.py
index 3d152a80742..8e8e44eeb5c 100644
--- a/src/pip/_internal/cli/spinners.py
+++ b/src/pip/_internal/cli/spinners.py
@@ -106,7 +106,7 @@ def finish(self, final_status):
         # type: (str) -> None
         if self._finished:
             return
-        self._update("finished with status '%s'" % (final_status,))
+        self._update("finished with status '{final_status}'".format(**locals()))
         self._finished = True
 
 
diff --git a/src/pip/_internal/commands/completion.py b/src/pip/_internal/commands/completion.py
index e0b743e542f..d3469131090 100644
--- a/src/pip/_internal/commands/completion.py
+++ b/src/pip/_internal/commands/completion.py
@@ -10,7 +10,7 @@
 from pip._internal.utils.misc import get_prog
 
 BASE_COMPLETION = """
-# pip %(shell)s completion start%(script)s# pip %(shell)s completion end
+# pip {shell} completion start{script}# pip {shell} completion end
 """
 
 COMPLETION_SCRIPTS = {
@@ -21,7 +21,7 @@
                            COMP_CWORD=$COMP_CWORD \\
                            PIP_AUTO_COMPLETE=1 $1 2>/dev/null ) )
         }
-        complete -o default -F _pip_completion %(prog)s
+        complete -o default -F _pip_completion {prog}
     """,
     'zsh': """
         function _pip_completion {
@@ -32,7 +32,7 @@
                      COMP_CWORD=$(( cword-1 )) \\
                      PIP_AUTO_COMPLETE=1 $words[1] 2>/dev/null ))
         }
-        compctl -K _pip_completion %(prog)s
+        compctl -K _pip_completion {prog}
     """,
     'fish': """
         function __fish_complete_pip
@@ -43,7 +43,7 @@
             set -lx PIP_AUTO_COMPLETE 1
             string split \\  -- (eval $COMP_WORDS[1])
         end
-        complete -fa "(__fish_complete_pip)" -c %(prog)s
+        complete -fa "(__fish_complete_pip)" -c {prog}
     """,
 }
 
@@ -85,11 +85,9 @@ def run(self, options, args):
         shell_options = ['--' + shell for shell in sorted(shells)]
         if options.shell in shells:
             script = textwrap.dedent(
-                COMPLETION_SCRIPTS.get(options.shell, '') % {
-                    'prog': get_prog(),
-                }
+                COMPLETION_SCRIPTS.get(options.shell, '').format(prog=get_prog())
             )
-            print(BASE_COMPLETION % {'script': script, 'shell': options.shell})
+            print(BASE_COMPLETION.format(script=script, shell=options.shell))
         else:
             sys.stderr.write(
                 'ERROR: You must pass {}\n' .format(' or '.join(shell_options))
diff --git a/src/pip/_internal/commands/search.py b/src/pip/_internal/commands/search.py
index 2e880eec224..276379ca640 100644
--- a/src/pip/_internal/commands/search.py
+++ b/src/pip/_internal/commands/search.py
@@ -121,8 +121,9 @@ def print_results(hits, name_column_width=None, terminal_width=None):
                 summary = textwrap.wrap(summary, target_width)
                 summary = ('\n' + ' ' * (name_column_width + 3)).join(summary)
 
-        line = '%-*s - %s' % (name_column_width,
-                              '%s (%s)' % (name, latest), summary)
+        line = '{name_latest:{name_column_width}} - {summary}'.format(
+            name_latest='{name} ({latest})'.format(**locals()),
+            **locals)
         try:
             write_output(line)
             if name in installed_packages:
diff --git a/src/pip/_internal/commands/uninstall.py b/src/pip/_internal/commands/uninstall.py
index e93ad74e29e..5db4fb46721 100644
--- a/src/pip/_internal/commands/uninstall.py
+++ b/src/pip/_internal/commands/uninstall.py
@@ -73,8 +73,8 @@ def run(self, options, args):
                     reqs_to_uninstall[canonicalize_name(req.name)] = req
         if not reqs_to_uninstall:
             raise InstallationError(
-                'You must give at least one requirement to %(name)s (see '
-                '"pip help %(name)s")' % dict(name=self.name)
+                'You must give at least one requirement to {self.name} (see '
+                '"pip help {self.name}")'.format(**locals())
             )
 
         protect_pip_from_modification_on_windows(
diff --git a/src/pip/_internal/models/link.py b/src/pip/_internal/models/link.py
index 0b30ab2511a..ed057de196b 100644
--- a/src/pip/_internal/models/link.py
+++ b/src/pip/_internal/models/link.py
@@ -96,7 +96,7 @@ def filename(self):
             return netloc
 
         name = urllib_parse.unquote(name)
-        assert name, ('URL %r produced no filename' % self._url)
+        assert name, ('URL {self._url!r} produced no filename'.format(**locals()))
         return name
 
     @property
diff --git a/src/pip/_internal/operations/install/wheel.py b/src/pip/_internal/operations/install/wheel.py
index b1a76a24ce2..6184499bdd2 100644
--- a/src/pip/_internal/operations/install/wheel.py
+++ b/src/pip/_internal/operations/install/wheel.py
@@ -534,13 +534,9 @@ def is_entrypoint_wrapper(name):
             del console[k]
 
     # Generate the console and GUI entry points specified in the wheel
-    scripts_to_generate.extend(
-        '%s = %s' % kv for kv in console.items()
-    )
+    scripts_to_generate.extend(map('{} = {}'.format, console.items()))
 
-    gui_scripts_to_generate = [
-        '%s = %s' % kv for kv in gui.items()
-    ]
+    gui_scripts_to_generate = list(map('{} = {}'.format, gui.items()))
 
     generated_console_scripts = []  # type: List[str]
 
diff --git a/src/pip/_internal/req/constructors.py b/src/pip/_internal/req/constructors.py
index 395157c4be6..195b0d0be78 100644
--- a/src/pip/_internal/req/constructors.py
+++ b/src/pip/_internal/req/constructors.py
@@ -281,8 +281,8 @@ def _get_url_from_path(path, name):
         if is_installable_dir(path):
             return path_to_url(path)
         raise InstallationError(
-            "Directory %r is not installable. Neither 'setup.py' "
-            "nor 'pyproject.toml' found." % name
+            "Directory {name!r} is not installable. Neither 'setup.py' "
+            "nor 'pyproject.toml' found.".format(**locals())
         )
     if not is_archive_file(path):
         return None
@@ -339,7 +339,7 @@ def parse_req_from_line(name, line_source):
         # wheel file
         if link.is_wheel:
             wheel = Wheel(link.filename)  # can raise InvalidWheelFilename
-            req_as_string = "%s==%s" % (wheel.name, wheel.version)
+            req_as_string = "{wheel.name}=={wheel.version}".format(**locals())
         else:
             # set the req to the egg fragment.  when it's not there, this
             # will become an 'unnamed' requirement
diff --git a/src/pip/_internal/req/req_install.py b/src/pip/_internal/req/req_install.py
index 5926a17de89..ce0309932cb 100644
--- a/src/pip/_internal/req/req_install.py
+++ b/src/pip/_internal/req/req_install.py
@@ -639,7 +639,7 @@ def update_editable(self, obtain=True):
         if self.link.scheme == 'file':
             # Static paths don't get updated
             return
-        assert '+' in self.link.url, "bad url: %r" % self.link.url
+        assert '+' in self.link.url, "bad url: {self.link.url!r}".format(**locals())
         vc_type, url = self.link.url.split('+', 1)
         vcs_backend = vcs.get_backend(vc_type)
         if vcs_backend:
@@ -701,7 +701,8 @@ def _get_archive_name(self, path, parentdir, rootdir):
         def _clean_zip_name(name, prefix):
             # type: (str, str) -> str
             assert name.startswith(prefix + os.path.sep), (
-                "name %r doesn't start with prefix %r" % (name, prefix)
+                "name {name!r} doesn't start with prefix {prefix!r}"
+                .format(**locals())
             )
             name = name[len(prefix) + 1:]
             name = name.replace(os.path.sep, '/')
diff --git a/src/pip/_internal/req/req_set.py b/src/pip/_internal/req/req_set.py
index dc76cce9b30..bc8e32264a3 100644
--- a/src/pip/_internal/req/req_set.py
+++ b/src/pip/_internal/req/req_set.py
@@ -194,7 +194,7 @@ def get_requirement(self, name):
         if project_name in self.requirements:
             return self.requirements[project_name]
 
-        raise KeyError("No project with the name %r" % name)
+        raise KeyError("No project with the name {name!r}".format(**locals()))
 
     @property
     def all_requirements(self):
diff --git a/src/pip/_internal/utils/compat.py b/src/pip/_internal/utils/compat.py
index 08c292d189d..d939e21fe2a 100644
--- a/src/pip/_internal/utils/compat.py
+++ b/src/pip/_internal/utils/compat.py
@@ -64,7 +64,7 @@ def backslashreplace_decode_fn(err):
         raw_bytes = (err.object[i] for i in range(err.start, err.end))
         # Python 2 gave us characters - convert to numeric bytes
         raw_bytes = (ord(b) for b in raw_bytes)
-        return u"".join(u"\\x%x" % c for c in raw_bytes), err.end
+        return u"".join(map(u"\\x{:x}".format, raw_bytes)), err.end
     codecs.register_error(
         "backslashreplace_decode",
         backslashreplace_decode_fn,
diff --git a/src/pip/_internal/utils/filesystem.py b/src/pip/_internal/utils/filesystem.py
index 6f1537e4032..a0866779719 100644
--- a/src/pip/_internal/utils/filesystem.py
+++ b/src/pip/_internal/utils/filesystem.py
@@ -73,7 +73,7 @@ def copy2_fixed(src, dest):
                 pass
             else:
                 if is_socket_file:
-                    raise shutil.SpecialFileError("`%s` is a socket" % f)
+                    raise shutil.SpecialFileError("`{f}` is a socket".format(**locals()))
 
         raise
 
diff --git a/src/pip/_internal/utils/logging.py b/src/pip/_internal/utils/logging.py
index 7767111a6ba..54ff956a38f 100644
--- a/src/pip/_internal/utils/logging.py
+++ b/src/pip/_internal/utils/logging.py
@@ -156,7 +156,7 @@ def format(self, record):
         if self.add_timestamp:
             # TODO: Use Formatter.default_time_format after dropping PY2.
             t = self.formatTime(record, "%Y-%m-%dT%H:%M:%S")
-            prefix = '%s,%03d ' % (t, record.msecs)
+            prefix = '{t},{record.msecs:03} '.format(**locals())
         prefix += " " * get_indentation()
         formatted = "".join([
             prefix + line
diff --git a/src/pip/_internal/utils/misc.py b/src/pip/_internal/utils/misc.py
index 5ad0544be79..ae3561fa8cc 100644
--- a/src/pip/_internal/utils/misc.py
+++ b/src/pip/_internal/utils/misc.py
@@ -266,13 +266,13 @@ def ask_password(message):
 def format_size(bytes):
     # type: (float) -> str
     if bytes > 1000 * 1000:
-        return '%.1f MB' % (bytes / 1000.0 / 1000)
+        return '{:.1} MB'.format(bytes / 1000.0 / 1000)
     elif bytes > 10 * 1000:
-        return '%i kB' % (bytes / 1000)
+        return '{} kB'.format(int(bytes / 1000))
     elif bytes > 1000:
-        return '%.1f kB' % (bytes / 1000.0)
+        return '{:.1} kB'.format(bytes / 1000.0)
     else:
-        return '%i bytes' % bytes
+        return '{} bytes'.format(int(bytes))
 
 
 def is_installable_dir(path):
diff --git a/src/pip/_internal/utils/urls.py b/src/pip/_internal/utils/urls.py
index 9ad40feb345..a3dcc83b527 100644
--- a/src/pip/_internal/utils/urls.py
+++ b/src/pip/_internal/utils/urls.py
@@ -34,7 +34,7 @@ def url_to_path(url):
     Convert a file: URL to a path.
     """
     assert url.startswith('file:'), (
-        "You can only turn file: urls into filenames (not %r)" % url)
+        "You can only turn file: urls into filenames (not {url!r})".format(**locals()))
 
     _, netloc, path, _, _ = urllib_parse.urlsplit(url)
 
@@ -46,8 +46,8 @@ def url_to_path(url):
         netloc = '\\\\' + netloc
     else:
         raise ValueError(
-            'non-local file URIs are not supported on this platform: %r'
-            % url
+            'non-local file URIs are not supported on this platform: {url!r}'
+            .format(**locals())
         )
 
     path = urllib_request.url2pathname(netloc + path)
diff --git a/src/pip/_internal/vcs/subversion.py b/src/pip/_internal/vcs/subversion.py
index 6c76d1ad435..064fb77e50e 100644
--- a/src/pip/_internal/vcs/subversion.py
+++ b/src/pip/_internal/vcs/subversion.py
@@ -151,7 +151,7 @@ def _get_svn_url_rev(cls, location):
         elif data.startswith('<?xml'):
             match = _svn_xml_url_re.search(data)
             if not match:
-                raise ValueError('Badly formatted data: %r' % data)
+                raise ValueError('Badly formatted data: {data!r}'.format(**locals()))
             url = match.group(1)    # get repository URL
             revs = [int(m.group(1)) for m in _svn_rev_re.finditer(data)] + [0]
         else:
diff --git a/src/pip/_internal/vcs/versioncontrol.py b/src/pip/_internal/vcs/versioncontrol.py
index 7b6171451ac..da53827cd46 100644
--- a/src/pip/_internal/vcs/versioncontrol.py
+++ b/src/pip/_internal/vcs/versioncontrol.py
@@ -683,9 +683,9 @@ def run_command(
             # In other words, the VCS executable isn't available
             if e.errno == errno.ENOENT:
                 raise BadCommand(
-                    'Cannot find command %r - do you have '
-                    '%r installed and in your '
-                    'PATH?' % (cls.name, cls.name))
+                    'Cannot find command {cls.name!r} - do you have '
+                    '{cls.name!r} installed and in your '
+                    'PATH?'.format(**locals()))
             else:
                 raise  # re-raise exception if a different error occurred
 
diff --git a/tests/conftest.py b/tests/conftest.py
index 3430e271d77..f539bb32be2 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -234,11 +234,11 @@ def not_code_files_and_folders(path, names):
 
 
 def _common_wheel_editable_install(tmpdir_factory, common_wheels, package):
-    wheel_candidates = list(common_wheels.glob('%s-*.whl' % package))
+    wheel_candidates = list(common_wheels.glob('{package}-*.whl'.format(**locals())))
     assert len(wheel_candidates) == 1, wheel_candidates
     install_dir = Path(str(tmpdir_factory.mktemp(package))) / 'install'
     Wheel(wheel_candidates[0]).install_as_egg(install_dir)
-    (install_dir / 'EGG-INFO').rename(install_dir / '%s.egg-info' % package)
+    (install_dir / 'EGG-INFO').rename(install_dir / '{package}.egg-info'.format(**locals()))
     assert compileall.compile_dir(str(install_dir), quiet=1)
     return install_dir
 
diff --git a/tests/data/src/chattymodule/setup.py b/tests/data/src/chattymodule/setup.py
index 7211972d1a7..01d7720765f 100644
--- a/tests/data/src/chattymodule/setup.py
+++ b/tests/data/src/chattymodule/setup.py
@@ -5,7 +5,7 @@
 
 from setuptools import setup
 
-print("HELLO FROM CHATTYMODULE %s" % (sys.argv[1],))
+print("HELLO FROM CHATTYMODULE {sys.argv[1]}".format(**locals()))
 print(os.environ)
 print(sys.argv)
 if "--fail" in sys.argv:
diff --git a/tests/functional/test_completion.py b/tests/functional/test_completion.py
index 4eaf36b4c85..a3986811b6f 100644
--- a/tests/functional/test_completion.py
+++ b/tests/functional/test_completion.py
@@ -230,7 +230,7 @@ def test_completion_not_files_after_nonexpecting_option(
     (e.g. ``pip install``)
     """
     res, env = autocomplete(
-        words=('pip install %s r' % cl_opts),
+        words=('pip install {cl_opts} r'.format(**locals())),
         cword='2',
         cwd=data.completion_paths,
     )
diff --git a/tests/functional/test_freeze.py b/tests/functional/test_freeze.py
index 3542e7754ef..c4842b7ac51 100644
--- a/tests/functional/test_freeze.py
+++ b/tests/functional/test_freeze.py
@@ -40,7 +40,7 @@ def _check_output(result, expected):
     actual = distribute_re.sub('', actual)
 
     def banner(msg):
-        return '\n========== %s ==========\n' % msg
+        return '\n========== {msg} ==========\n'.format(**locals())
 
     assert checker.check_output(expected, actual, ELLIPSIS), (
         banner('EXPECTED') + expected + banner('ACTUAL') + actual +
@@ -246,15 +246,15 @@ def test_freeze_git_clone(script, tmpdir):
     _check_output(result.stdout, expected)
 
     result = script.pip(
-        'freeze', '-f', '%s#egg=pip_test_package' % repo_dir,
+        'freeze', '-f', '{repo_dir}#egg=pip_test_package'.format(**locals()),
         expect_stderr=True,
     )
     expected = textwrap.dedent(
         """
-            -f %(repo)s#egg=pip_test_package...
+            -f {repo}#egg=pip_test_package...
             -e git+...#egg=version_pkg
             ...
-        """ % {'repo': repo_dir},
+        """.format(repo=repo_dir),
     ).strip()
     _check_output(result.stdout, expected)
 
@@ -311,15 +311,15 @@ def test_freeze_git_clone_srcdir(script, tmpdir):
     _check_output(result.stdout, expected)
 
     result = script.pip(
-        'freeze', '-f', '%s#egg=pip_test_package' % repo_dir,
+        'freeze', '-f', '{repo_dir}#egg=pip_test_package'.format(**locals()),
         expect_stderr=True,
     )
     expected = textwrap.dedent(
         """
-            -f %(repo)s#egg=pip_test_package...
+            -f {repo}#egg=pip_test_package...
             -e git+...#egg=version_pkg&subdirectory=subdir
             ...
-        """ % {'repo': repo_dir},
+        """.format(repo=repo_dir),
     ).strip()
     _check_output(result.stdout, expected)
 
@@ -352,14 +352,14 @@ def test_freeze_mercurial_clone_srcdir(script, tmpdir):
     _check_output(result.stdout, expected)
 
     result = script.pip(
-        'freeze', '-f', '%s#egg=pip_test_package' % repo_dir
+        'freeze', '-f', '{repo_dir}#egg=pip_test_package'.format(**locals())
     )
     expected = textwrap.dedent(
         """
-            -f %(repo)s#egg=pip_test_package...
+            -f {repo}#egg=pip_test_package...
             -e hg+...#egg=version_pkg&subdirectory=subdir
             ...
-        """ % {'repo': repo_dir},
+        """.format(repo=repo_dir),
     ).strip()
     _check_output(result.stdout, expected)
 
@@ -446,15 +446,15 @@ def test_freeze_mercurial_clone(script, tmpdir):
     _check_output(result.stdout, expected)
 
     result = script.pip(
-        'freeze', '-f', '%s#egg=pip_test_package' % repo_dir,
+        'freeze', '-f', '{repo_dir}#egg=pip_test_package'.format(**locals()),
         expect_stderr=True,
     )
     expected = textwrap.dedent(
         """
-            -f %(repo)s#egg=pip_test_package...
+            -f {repo}#egg=pip_test_package...
             ...-e hg+...#egg=version_pkg
             ...
-        """ % {'repo': repo_dir},
+        """.format(repo=repo_dir),
     ).strip()
     _check_output(result.stdout, expected)
 
@@ -468,7 +468,7 @@ def test_freeze_bazaar_clone(script, tmpdir):
     try:
         checkout_path = _create_test_package(script, vcs='bazaar')
     except OSError as e:
-        pytest.fail('Invoking `bzr` failed: %s' % e)
+        pytest.fail('Invoking `bzr` failed: {e}'.format(**locals()))
 
     result = script.run(
         'bzr', 'checkout', checkout_path, 'bzr-package'
@@ -486,13 +486,13 @@ def test_freeze_bazaar_clone(script, tmpdir):
 
     result = script.pip(
         'freeze', '-f',
-        '%s/#egg=django-wikiapp' % checkout_path,
+        '{checkout_path}/#egg=django-wikiapp'.format(**locals()),
         expect_stderr=True,
     )
     expected = textwrap.dedent("""\
-        -f %(repo)s/#egg=django-wikiapp
+        -f {repo}/#egg=django-wikiapp
         ...-e bzr+file://...@...#egg=version_pkg
-        ...""" % {'repo': checkout_path})
+        ...""".format(repo=checkout_path))
     _check_output(result.stdout, expected)
 
 
diff --git a/tests/functional/test_install.py b/tests/functional/test_install.py
index 1ea9db26e4b..8f52384d888 100644
--- a/tests/functional/test_install.py
+++ b/tests/functional/test_install.py
@@ -80,9 +80,9 @@ def test_pep518_refuses_conflicting_requires(script, data):
                                       project_dir, expect_error=True)
     assert (
         result.returncode != 0 and
-        ('Some build dependencies for %s conflict with PEP 517/518 supported '
+        ('Some build dependencies for {url} conflict with PEP 517/518 supported '
          'requirements: setuptools==1.0 is incompatible with '
-         'setuptools>=40.8.0.' % path_to_url(project_dir)) in result.stderr
+         'setuptools>=40.8.0.'.format(url=path_to_url(project_dir))) in result.stderr
     ), str(result)
 
 
@@ -198,12 +198,12 @@ def test_pip_second_command_line_interface_works(
     if pyversion_tuple < (2, 7, 9):
         kwargs['expect_stderr'] = True
 
-    args = ['pip%s' % pyversion]
+    args = ['pip{version}'.format(**locals())]
     args.extend(['install', 'INITools==0.2'])
     args.extend(['-f', data.packages])
     result = script.run(*args, **kwargs)
     egg_info_folder = (
-        script.site_packages / 'INITools-0.2-py%s.egg-info' % pyversion
+        script.site_packages / 'INITools-0.2-py{pyversion}.egg-info'.format(**locals())
     )
     initools_folder = script.site_packages / 'initools'
     assert egg_info_folder in result.files_created, str(result)
@@ -234,7 +234,7 @@ def test_basic_install_from_pypi(script):
     """
     result = script.pip('install', 'INITools==0.2')
     egg_info_folder = (
-        script.site_packages / 'INITools-0.2-py%s.egg-info' % pyversion
+        script.site_packages / 'INITools-0.2-py{pyversion}.egg-info'.format(**locals())
     )
     initools_folder = script.site_packages / 'initools'
     assert egg_info_folder in result.files_created, str(result)
@@ -281,7 +281,7 @@ def test_basic_install_editable_from_svn(script):
 def _test_install_editable_from_git(script, tmpdir):
     """Test cloning from Git."""
     pkg_path = _create_test_package(script, name='testpackage', vcs='git')
-    args = ['install', '-e', 'git+%s#egg=testpackage' % path_to_url(pkg_path)]
+    args = ['install', '-e', 'git+{url}#egg=testpackage'.format(url=path_to_url(pkg_path))]
     result = script.pip(*args)
     result.assert_installed('testpackage', with_files=['.git'])
 
@@ -310,10 +310,10 @@ def test_install_editable_uninstalls_existing(data, script, tmpdir):
 
     result = script.pip(
         'install', '-e',
-        '%s#egg=pip-test-package' %
-        local_checkout(
+        '{dir}#egg=pip-test-package'.format(
+            dir=local_checkout(
             'git+https://github.com/pypa/pip-test-package.git', tmpdir,
-        ),
+        )),
     )
     result.assert_installed('pip-test-package', with_files=['.git'])
     assert 'Found existing installation: pip-test-package 0.1' in result.stdout
@@ -362,7 +362,7 @@ def test_vcs_url_final_slash_normalization(script, tmpdir):
     Test that presence or absence of final slash in VCS URL is normalized.
     """
     pkg_path = _create_test_package(script, name='testpackage', vcs='hg')
-    args = ['install', '-e', 'hg+%s/#egg=testpackage' % path_to_url(pkg_path)]
+    args = ['install', '-e', 'hg+{url}/#egg=testpackage'.format(url=path_to_url(pkg_path))]
     result = script.pip(*args)
     result.assert_installed('testpackage', with_files=['.hg'])
 
@@ -371,7 +371,7 @@ def test_vcs_url_final_slash_normalization(script, tmpdir):
 def test_install_editable_from_bazaar(script, tmpdir):
     """Test checking out from Bazaar."""
     pkg_path = _create_test_package(script, name='testpackage', vcs='bazaar')
-    args = ['install', '-e', 'bzr+%s/#egg=testpackage' % path_to_url(pkg_path)]
+    args = ['install', '-e', 'bzr+{url}/#egg=testpackage'.format(url=path_to_url(pkg_path))]
     result = script.pip(*args)
     result.assert_installed('testpackage', with_files=['.bzr'])
 
@@ -384,12 +384,12 @@ def test_vcs_url_urlquote_normalization(script, tmpdir):
     """
     script.pip(
         'install', '-e',
-        '%s/#egg=django-wikiapp' %
-        local_checkout(
-            'bzr+http://bazaar.launchpad.net/%7Edjango-wikiapp/django-wikiapp'
-            '/release-0.1',
-            tmpdir,
-        ),
+        '{url}/#egg=django-wikiapp'.format(
+            url=local_checkout(
+                'bzr+http://bazaar.launchpad.net/%7Edjango-wikiapp/django-wikiapp'
+                '/release-0.1',
+                tmpdir,
+            )),
     )
 
 
@@ -401,7 +401,8 @@ def test_basic_install_from_local_directory(script, data):
     result = script.pip('install', to_install)
     fspkg_folder = script.site_packages / 'fspkg'
     egg_info_folder = (
-        script.site_packages / 'FSPkg-0.1.dev0-py%s.egg-info' % pyversion
+        script.site_packages /
+        'FSPkg-0.1.dev0-py{pyversion}.egg-info'.format(**locals())
     )
     assert fspkg_folder in result.files_created, str(result.stdout)
     assert egg_info_folder in result.files_created, str(result)
@@ -420,7 +421,7 @@ def test_basic_install_relative_directory(script, data, test_type, editable):
     Test installing a requirement using a relative path.
     """
     egg_info_file = (
-        script.site_packages / 'FSPkg-0.1.dev0-py%s.egg-info' % pyversion
+        script.site_packages / 'FSPkg-0.1.dev0-py{pyversion}.egg-info'.format(**locals())
     )
     egg_link_file = (
         script.site_packages / 'FSPkg.egg-link'
@@ -550,7 +551,8 @@ def test_install_from_local_directory_with_symlinks_to_directories(
     result = script.pip('install', to_install)
     pkg_folder = script.site_packages / 'symlinks'
     egg_info_folder = (
-        script.site_packages / 'symlinks-0.1.dev0-py%s.egg-info' % pyversion
+        script.site_packages /
+        'symlinks-0.1.dev0-py{pyversion}.egg-info'.format(**locals())
     )
     assert pkg_folder in result.files_created, str(result.stdout)
     assert egg_info_folder in result.files_created, str(result)
@@ -562,7 +564,8 @@ def test_install_from_local_directory_with_socket_file(script, data, tmpdir):
     Test installing from a local directory containing a socket file.
     """
     egg_info_file = (
-        script.site_packages / "FSPkg-0.1.dev0-py%s.egg-info" % pyversion
+        script.site_packages /
+        "FSPkg-0.1.dev0-py{pyversion}.egg-info".format(**locals())
     )
     package_folder = script.site_packages / "fspkg"
     to_copy = data.packages.joinpath("FSPkg")
@@ -663,7 +666,7 @@ def test_install_curdir(script, data):
     result = script.pip('install', curdir, cwd=run_from)
     fspkg_folder = script.site_packages / 'fspkg'
     egg_info_folder = (
-        script.site_packages / 'FSPkg-0.1.dev0-py%s.egg-info' % pyversion
+        script.site_packages / 'FSPkg-0.1.dev0-py{pyversion}.egg-info'.format(**locals())
     )
     assert fspkg_folder in result.files_created, str(result.stdout)
     assert egg_info_folder in result.files_created, str(result)
@@ -677,7 +680,7 @@ def test_install_pardir(script, data):
     result = script.pip('install', pardir, cwd=run_from)
     fspkg_folder = script.site_packages / 'fspkg'
     egg_info_folder = (
-        script.site_packages / 'FSPkg-0.1.dev0-py%s.egg-info' % pyversion
+        script.site_packages / 'FSPkg-0.1.dev0-py{pyversion}.egg-info'.format(**locals())
     )
     assert fspkg_folder in result.files_created, str(result.stdout)
     assert egg_info_folder in result.files_created, str(result)
@@ -714,9 +717,9 @@ def test_install_using_install_option_and_editable(script, tmpdir):
     script.scratch_path.joinpath(folder).mkdir()
     url = 'git+git://github.com/pypa/pip-test-package'
     result = script.pip(
-        'install', '-e', '%s#egg=pip-test-package' %
-        local_checkout(url, tmpdir),
-        '--install-option=--script-dir=%s' % folder,
+        'install', '-e', '{url}#egg=pip-test-package'
+        .format(url=local_checkout(url, tmpdir)),
+        '--install-option=--script-dir={footer}'.format(**locals()),
         expect_stderr=True)
     script_file = (
         script.venv / 'src' / 'pip-test-package' /
@@ -735,7 +738,7 @@ def test_install_global_option_using_editable(script, tmpdir):
     url = 'hg+http://bitbucket.org/runeh/anyjson'
     result = script.pip(
         'install', '--global-option=--version', '-e',
-        '%s@0.2.5#egg=anyjson' % local_checkout(url, tmpdir),
+        '{url}@0.2.5#egg=anyjson'.format(url=local_checkout(url, tmpdir)),
         expect_stderr=True)
     assert 'Successfully installed anyjson' in result.stdout
 
@@ -747,7 +750,7 @@ def test_install_package_with_same_name_in_curdir(script):
     """
     script.scratch_path.joinpath("mock==0.6").mkdir()
     result = script.pip('install', 'mock==0.6')
-    egg_folder = script.site_packages / 'mock-0.6.0-py%s.egg-info' % pyversion
+    egg_folder = script.site_packages / 'mock-0.6.0-py{pyversion}.egg-info'.format(**locals())
     assert egg_folder in result.files_created, str(result)
 
 
@@ -765,7 +768,7 @@ def test_install_folder_using_dot_slash(script):
     pkg_path = script.scratch_path / 'mock'
     pkg_path.joinpath("setup.py").write_text(mock100_setup_py)
     result = script.pip('install', './mock')
-    egg_folder = script.site_packages / 'mock-100.1-py%s.egg-info' % pyversion
+    egg_folder = script.site_packages / 'mock-100.1-py{pyversion}.egg-info'.format(**locals())
     assert egg_folder in result.files_created, str(result)
 
 
@@ -777,7 +780,7 @@ def test_install_folder_using_slash_in_the_end(script):
     pkg_path = script.scratch_path / 'mock'
     pkg_path.joinpath("setup.py").write_text(mock100_setup_py)
     result = script.pip('install', 'mock' + os.path.sep)
-    egg_folder = script.site_packages / 'mock-100.1-py%s.egg-info' % pyversion
+    egg_folder = script.site_packages / 'mock-100.1-py{pyversion}.egg-info'.format(**locals())
     assert egg_folder in result.files_created, str(result)
 
 
@@ -790,7 +793,7 @@ def test_install_folder_using_relative_path(script):
     pkg_path = script.scratch_path / 'initools' / 'mock'
     pkg_path.joinpath("setup.py").write_text(mock100_setup_py)
     result = script.pip('install', Path('initools') / 'mock')
-    egg_folder = script.site_packages / 'mock-100.1-py%s.egg-info' % pyversion
+    egg_folder = script.site_packages / 'mock-100.1-py{pyversion}.egg-info'.format(**locals())
     assert egg_folder in result.files_created, str(result)
 
 
@@ -802,8 +805,8 @@ def test_install_package_which_contains_dev_in_name(script):
     result = script.pip('install', 'django-devserver==0.0.4')
     devserver_folder = script.site_packages / 'devserver'
     egg_info_folder = (
-        script.site_packages / 'django_devserver-0.0.4-py%s.egg-info' %
-        pyversion
+        script.site_packages /
+        'django_devserver-0.0.4-py{pyversion}.egg-info'.format(**locals)
     )
     assert devserver_folder in result.files_created, str(result.stdout)
     assert egg_info_folder in result.files_created, str(result)
@@ -832,7 +835,7 @@ def test_install_package_with_target(script):
         str(result)
     )
     egg_folder = (
-        Path('scratch') / 'target' / 'simple-2.0-py%s.egg-info' % pyversion)
+        Path('scratch') / 'target' / 'simple-2.0-py{pyversion}.egg-info'.format(**locals()))
     assert egg_folder in result.files_created, (
         str(result)
     )
@@ -966,8 +969,8 @@ def test_install_package_with_root(script, data):
         'simple==1.0',
     )
     normal_install_path = (
-        script.base_path / script.site_packages / 'simple-1.0-py%s.egg-info' %
-        pyversion
+        script.base_path / script.site_packages /
+        'simple-1.0-py{pyversion}.egg-info'.format(**locals())
     )
     # use distutils to change the root exactly how the --root option does it
     from distutils.util import change_root
@@ -1090,9 +1093,9 @@ def test_url_req_case_mismatch_no_index(script, data):
     )
 
     # only Upper-1.0.tar.gz should get installed.
-    egg_folder = script.site_packages / 'Upper-1.0-py%s.egg-info' % pyversion
+    egg_folder = script.site_packages / 'Upper-1.0-py{pyversion}.egg-info'.format(**locals())
     assert egg_folder in result.files_created, str(result)
-    egg_folder = script.site_packages / 'Upper-2.0-py%s.egg-info' % pyversion
+    egg_folder = script.site_packages / 'Upper-2.0-py{pyversion}.egg-info'.format(**locals())
     assert egg_folder not in result.files_created, str(result)
 
 
@@ -1117,9 +1120,9 @@ def test_url_req_case_mismatch_file_index(script, data):
     )
 
     # only Upper-1.0.tar.gz should get installed.
-    egg_folder = script.site_packages / 'Dinner-1.0-py%s.egg-info' % pyversion
+    egg_folder = script.site_packages / 'Dinner-1.0-py{pyversion}.egg-info'.format(**locals())
     assert egg_folder in result.files_created, str(result)
-    egg_folder = script.site_packages / 'Dinner-2.0-py%s.egg-info' % pyversion
+    egg_folder = script.site_packages / 'Dinner-2.0-py{pyversion}.egg-info'.format(**locals())
     assert egg_folder not in result.files_created, str(result)
 
 
@@ -1134,9 +1137,9 @@ def test_url_incorrect_case_no_index(script, data):
     )
 
     # only Upper-2.0.tar.gz should get installed.
-    egg_folder = script.site_packages / 'Upper-1.0-py%s.egg-info' % pyversion
+    egg_folder = script.site_packages / 'Upper-1.0-py{pyversion}.egg-info'.format(**locals())
     assert egg_folder not in result.files_created, str(result)
-    egg_folder = script.site_packages / 'Upper-2.0-py%s.egg-info' % pyversion
+    egg_folder = script.site_packages / 'Upper-2.0-py{pyversion}.egg-info'.format(**locals())
     assert egg_folder in result.files_created, str(result)
 
 
@@ -1152,9 +1155,9 @@ def test_url_incorrect_case_file_index(script, data):
     )
 
     # only Upper-2.0.tar.gz should get installed.
-    egg_folder = script.site_packages / 'Dinner-1.0-py%s.egg-info' % pyversion
+    egg_folder = script.site_packages / 'Dinner-1.0-py{pyversion}.egg-info'.format(**locals())
     assert egg_folder not in result.files_created, str(result)
-    egg_folder = script.site_packages / 'Dinner-2.0-py%s.egg-info' % pyversion
+    egg_folder = script.site_packages / 'Dinner-2.0-py{pyversion}.egg-info'.format(**locals())
     assert egg_folder in result.files_created, str(result)
 
     # Should show index-url location in output
@@ -1258,7 +1261,7 @@ def test_install_subprocess_output_handling(script, data):
 def test_install_log(script, data, tmpdir):
     # test that verbose logs go to "--log" file
     f = tmpdir.joinpath("log.txt")
-    args = ['--log=%s' % f,
+    args = ['--log={f}'.format(**locals()),
             'install', data.src.joinpath('chattymodule')]
     result = script.pip(*args)
     assert 0 == result.stdout.count("HELLO FROM CHATTYMODULE")
@@ -1411,7 +1414,7 @@ def test_install_editable_with_wrong_egg_name(script):
               version='0.1')
     """))
     result = script.pip(
-        'install', '--editable', 'file://%s#egg=pkgb' % pkga_path
+        'install', '--editable', 'file://{pkga_path}#egg=pkgb'.format(**locals())
     )
     assert ("Generating metadata for package pkgb produced metadata "
             "for project name pkga. Fix your #egg=pkgb "
@@ -1485,7 +1488,7 @@ def test_install_incompatible_python_requires_editable(script):
               version='0.1')
     """))
     result = script.pip(
-        'install', '--editable=%s' % pkga_path, expect_error=True)
+        'install', '--editable={pkga_path}'.format(**locals()), expect_error=True)
     assert _get_expected_error_text() in result.stderr, str(result)
 
 
@@ -1599,7 +1602,7 @@ def test_installed_files_recorded_in_deterministic_order(script, data):
     to_install = data.packages.joinpath("FSPkg")
     result = script.pip('install', to_install)
     fspkg_folder = script.site_packages / 'fspkg'
-    egg_info = 'FSPkg-0.1.dev0-py%s.egg-info' % pyversion
+    egg_info = 'FSPkg-0.1.dev0-py{pyversion}.egg-info'.format(**locals())
     installed_files_path = (
         script.site_packages / egg_info / 'installed-files.txt'
     )
@@ -1664,8 +1667,8 @@ def test_target_install_ignores_distutils_config_install_prefix(script):
     distutils_config.write_text(textwrap.dedent(
         '''
         [install]
-        prefix=%s
-        ''' % str(prefix)))
+        prefix={prefix}
+        '''.format(**locals())))
     target = script.scratch_path / 'target'
     result = script.pip_install_local('simplewheel', '-t', target)
 
diff --git a/tests/functional/test_install_cleanup.py b/tests/functional/test_install_cleanup.py
index b07c809079b..7f91be3a4b8 100644
--- a/tests/functional/test_install_cleanup.py
+++ b/tests/functional/test_install_cleanup.py
@@ -85,7 +85,7 @@ def test_cleanup_req_satisfied_no_name(script, data):
     script.pip('install', dist)
 
     build = script.venv_path / 'build'
-    assert not exists(build), "unexpected build/ dir exists: %s" % build
+    assert not exists(build), "unexpected build/ dir exists: {build}".format(**locals())
     script.assert_no_temp()
 
 
@@ -99,7 +99,7 @@ def test_cleanup_after_install_exception(script, data):
         expect_error=True,
     )
     build = script.venv_path / 'build'
-    assert not exists(build), "build/ dir still exists: %s" % result.stdout
+    assert not exists(build), "build/ dir still exists: {result.stdout}".format(**locals())
     script.assert_no_temp()
 
 
@@ -113,7 +113,7 @@ def test_cleanup_after_egg_info_exception(script, data):
         expect_error=True,
     )
     build = script.venv_path / 'build'
-    assert not exists(build), "build/ dir still exists: %s" % result.stdout
+    assert not exists(build), "build/ dir still exists: {result.stdout}".format(**locals())
     script.assert_no_temp()
 
 
diff --git a/tests/functional/test_install_compat.py b/tests/functional/test_install_compat.py
index b957934ef48..bd6baa496cc 100644
--- a/tests/functional/test_install_compat.py
+++ b/tests/functional/test_install_compat.py
@@ -24,17 +24,18 @@ def test_debian_egg_name_workaround(script):
     result = script.pip('install', 'INITools==0.2')
 
     egg_info = os.path.join(
-        script.site_packages, "INITools-0.2-py%s.egg-info" % pyversion)
+        script.site_packages,
+        "INITools-0.2-py{pyversion}.egg-info".format(**locals()))
 
     # Debian only removes pyversion for global installs, not inside a venv
     # so even if this test runs on a Debian/Ubuntu system with broken
     # setuptools, since our test runs inside a venv we'll still have the normal
     # .egg-info
-    assert egg_info in result.files_created, "Couldn't find %s" % egg_info
+    assert egg_info in result.files_created, "Couldn't find {egg_info}".format(**locals())
 
     # The Debian no-pyversion version of the .egg-info
     mangled = os.path.join(script.site_packages, "INITools-0.2.egg-info")
-    assert mangled not in result.files_created, "Found unexpected %s" % mangled
+    assert mangled not in result.files_created, "Found unexpected {mangled}".format(**locals())
 
     # Simulate a Debian install by copying the .egg-info to their name for it
     full_egg_info = os.path.join(script.base_path, egg_info)
diff --git a/tests/functional/test_install_config.py b/tests/functional/test_install_config.py
index 2b76e81cd25..088016a9f1b 100644
--- a/tests/functional/test_install_config.py
+++ b/tests/functional/test_install_config.py
@@ -107,7 +107,7 @@ def test_command_line_appends_correctly(script, data):
 
     """
     script.environ['PIP_FIND_LINKS'] = (
-        'https://test.pypi.org %s' % data.find_links
+        'https://test.pypi.org {data.find_links}'.format(**locals())
     )
     result = script.pip(
         'install', '-vvv', 'INITools', '--trusted-host',
diff --git a/tests/functional/test_install_extras.py b/tests/functional/test_install_extras.py
index acfd58dff17..bce95cb196d 100644
--- a/tests/functional/test_install_extras.py
+++ b/tests/functional/test_install_extras.py
@@ -121,7 +121,7 @@ def test_install_special_extra(script):
     """))
 
     result = script.pip(
-        'install', '--no-index', '%s[Hop_hOp-hoP]' % pkga_path,
+        'install', '--no-index', '{pkga_path}[Hop_hOp-hoP]'.format(**locals()),
         expect_error=True)
     assert (
         "Could not find a version that satisfies the requirement missing_pkg"
diff --git a/tests/functional/test_install_reqs.py b/tests/functional/test_install_reqs.py
index 2422bdb500e..2d83f5a6994 100644
--- a/tests/functional/test_install_reqs.py
+++ b/tests/functional/test_install_reqs.py
@@ -24,14 +24,14 @@ def test_requirements_file(script):
     script.scratch_path.joinpath("initools-req.txt").write_text(textwrap.dedent("""\
         INITools==0.2
         # and something else to test out:
-        %s<=%s
-        """ % (other_lib_name, other_lib_version)))
+        {other_lib_name}<={other_lib_version}
+        """.format(**locals())))
     result = script.pip(
         'install', '-r', script.scratch_path / 'initools-req.txt'
     )
     assert (
         script.site_packages / 'INITools-0.2-py{}.egg-info'.format(
-            pyversion in result.files_created)
+            pyversion) in result.files_created
     )
     assert script.site_packages / 'initools' in result.files_created
     assert result.files_created[script.site_packages / other_lib_name].dir
@@ -46,7 +46,7 @@ def test_schema_check_in_requirements_file(script):
 
     """
     script.scratch_path.joinpath("file-egg-req.txt").write_text(
-        "\n%s\n" % (
+        "\n{}\n".format(
             "git://github.com/alex/django-fixture-generator.git"
             "#egg=fixture_generator"
         )
@@ -73,7 +73,7 @@ def test_relative_requirements_file(script, data, test_type, editable):
 
     """
     egg_info_file = (
-        script.site_packages / 'FSPkg-0.1.dev0-py%s.egg-info' % pyversion
+        script.site_packages / 'FSPkg-0.1.dev0-py{pyversion}.egg-info'.format(**locals())
     )
     egg_link_file = (
         script.site_packages / 'FSPkg.egg-link'
@@ -120,22 +120,22 @@ def test_multiple_requirements_files(script, tmpdir):
     other_lib_name, other_lib_version = 'anyjson', '0.3'
     script.scratch_path.joinpath("initools-req.txt").write_text(
         textwrap.dedent("""
-            -e %s@10#egg=INITools
-            -r %s-req.txt
-        """) %
+            -e {}@10#egg=INITools
+            -r {}-req.txt
+        """).format
         (
             local_checkout('svn+http://svn.colorstudy.com/INITools', tmpdir),
             other_lib_name
         ),
     )
-    script.scratch_path.joinpath("%s-req.txt" % other_lib_name).write_text(
-        "%s<=%s" % (other_lib_name, other_lib_version)
+    script.scratch_path.joinpath("{other_lib_name}-req.txt".format(**locals())).write_text(
+        "{other_lib_name}<={other_lib_version}".format(**locals())
     )
     result = script.pip(
         'install', '-r', script.scratch_path / 'initools-req.txt'
     )
     assert result.files_created[script.site_packages / other_lib_name].dir
-    fn = '%s-%s-py%s.egg-info' % (other_lib_name, other_lib_version, pyversion)
+    fn = '{other_lib_name}-{other_lib_version}-py{pyversion}.egg-info'.format(**locals())
     assert result.files_created[script.site_packages / fn].dir
     assert script.venv / 'src' / 'initools' in result.files_created
 
@@ -176,13 +176,13 @@ def test_respect_order_in_requirements_file(script, data):
                   if 'Processing' in line]
 
     assert 'parent' in downloaded[0], (
-        'First download should be "parent" but was "%s"' % downloaded[0]
+        'First download should be "parent" but was "{}"'.format(downloaded[0])
     )
     assert 'child' in downloaded[1], (
-        'Second download should be "child" but was "%s"' % downloaded[1]
+        'Second download should be "child" but was "{}"'.format(downloaded[1])
     )
     assert 'simple' in downloaded[2], (
-        'Third download should be "simple" but was "%s"' % downloaded[2]
+        'Third download should be "simple" but was "{}"'.format(downloaded[2])
     )
 
 
@@ -215,8 +215,9 @@ def test_install_local_editable_with_subdirectory(script):
                                                               'version_subdir')
     result = script.pip(
         'install', '-e',
-        '%s#egg=version_subpkg&subdirectory=version_subdir' %
-        ('git+%s' % path_to_url(version_pkg_path),)
+        '{uri}#egg=version_subpkg&subdirectory=version_subdir'.format(
+            uri='git+' + path_to_url(version_pkg_path),
+        ),
     )
 
     result.assert_installed('version-subpkg', sub_dir='version_subdir')
@@ -228,8 +229,9 @@ def test_install_local_with_subdirectory(script):
                                                               'version_subdir')
     result = script.pip(
         'install',
-        '%s#egg=version_subpkg&subdirectory=version_subdir' %
-        ('git+' + path_to_url(version_pkg_path),)
+        '{uri}#egg=version_subpkg&subdirectory=version_subdir'.format(
+            uri='git+' + path_to_url(version_pkg_path),
+        ),
     )
 
     result.assert_installed('version_subpkg.py', editable=False)
@@ -247,7 +249,7 @@ def test_wheel_user_with_prefix_in_pydistutils_cfg(
     with open(user_cfg, "w") as cfg:
         cfg.write(textwrap.dedent("""
             [install]
-            prefix=%s""" % script.scratch_path))
+            prefix={script.scratch_path}""".format(**locals())))
 
     result = script.pip(
         'install', '--user', '--no-index',
@@ -268,13 +270,14 @@ def test_install_option_in_requirements_file(script, data, virtualenv):
 
     script.scratch_path.joinpath("reqs.txt").write_text(
         textwrap.dedent(
-            """simple --install-option='--home=%s'"""
-            % script.scratch_path.joinpath("home1")))
+            """simple --install-option='--home={home}'""".format(
+                home=script.scratch_path.joinpath("home1"))))
 
     result = script.pip(
         'install', '--no-index', '-f', data.find_links, '-r',
         script.scratch_path / 'reqs.txt',
-        '--install-option=--home=%s' % script.scratch_path.joinpath("home2"),
+        '--install-option=--home={home}'.format(
+            home=script.scratch_path.joinpath("home2")),
         expect_stderr=True)
 
     package_dir = script.scratch / 'home1' / 'lib' / 'python' / 'simple'
@@ -333,7 +336,7 @@ def test_constraints_local_install_causes_error(script, data):
 def test_constraints_constrain_to_local_editable(script, data):
     to_install = data.src.joinpath("singlemodule")
     script.scratch_path.joinpath("constraints.txt").write_text(
-        "-e %s#egg=singlemodule" % path_to_url(to_install)
+        "-e {url}#egg=singlemodule".format(url=path_to_url(to_install))
     )
     result = script.pip(
         'install', '--no-index', '-f', data.find_links, '-c',
@@ -344,7 +347,7 @@ def test_constraints_constrain_to_local_editable(script, data):
 def test_constraints_constrain_to_local(script, data):
     to_install = data.src.joinpath("singlemodule")
     script.scratch_path.joinpath("constraints.txt").write_text(
-        "%s#egg=singlemodule" % path_to_url(to_install)
+        "{url}#egg=singlemodule".format(url=path_to_url(to_install))
     )
     result = script.pip(
         'install', '--no-index', '-f', data.find_links, '-c',
@@ -400,7 +403,7 @@ def test_double_install_spurious_hash_mismatch(
 def test_install_with_extras_from_constraints(script, data):
     to_install = data.packages.joinpath("LocalExtras")
     script.scratch_path.joinpath("constraints.txt").write_text(
-        "%s#egg=LocalExtras[bar]" % path_to_url(to_install)
+        "{url}#egg=LocalExtras[bar]".format(url=path_to_url(to_install))
     )
     result = script.pip_install_local(
         '-c', script.scratch_path / 'constraints.txt', 'LocalExtras')
@@ -410,7 +413,7 @@ def test_install_with_extras_from_constraints(script, data):
 def test_install_with_extras_from_install(script, data):
     to_install = data.packages.joinpath("LocalExtras")
     script.scratch_path.joinpath("constraints.txt").write_text(
-        "%s#egg=LocalExtras" % path_to_url(to_install)
+        "{url}#egg=LocalExtras".format(url=path_to_url(to_install))
     )
     result = script.pip_install_local(
         '-c', script.scratch_path / 'constraints.txt', 'LocalExtras[baz]')
@@ -420,7 +423,7 @@ def test_install_with_extras_from_install(script, data):
 def test_install_with_extras_joined(script, data):
     to_install = data.packages.joinpath("LocalExtras")
     script.scratch_path.joinpath("constraints.txt").write_text(
-        "%s#egg=LocalExtras[bar]" % path_to_url(to_install)
+        "{url}#egg=LocalExtras[bar]".format(url=path_to_url(to_install))
     )
     result = script.pip_install_local(
         '-c', script.scratch_path / 'constraints.txt', 'LocalExtras[baz]'
@@ -432,7 +435,7 @@ def test_install_with_extras_joined(script, data):
 def test_install_with_extras_editable_joined(script, data):
     to_install = data.packages.joinpath("LocalExtras")
     script.scratch_path.joinpath("constraints.txt").write_text(
-        "-e %s#egg=LocalExtras[bar]" % path_to_url(to_install)
+        "-e {url}#egg=LocalExtras[bar]".format(url=path_to_url(to_install))
     )
     result = script.pip_install_local(
         '-c', script.scratch_path / 'constraints.txt', 'LocalExtras[baz]')
@@ -454,13 +457,15 @@ def test_install_distribution_duplicate_extras(script, data):
     package_name = to_install + "[bar]"
     with pytest.raises(AssertionError):
         result = script.pip_install_local(package_name, package_name)
-        assert 'Double requirement given: %s' % package_name in result.stderr
+        expected = (
+            'Double requirement given: {package_name}'.format(**locals()))
+        assert expected in result.stderr
 
 
 def test_install_distribution_union_with_constraints(script, data):
     to_install = data.packages.joinpath("LocalExtras")
     script.scratch_path.joinpath("constraints.txt").write_text(
-        "%s[bar]" % to_install)
+        "{to_install}[bar]".format(**locals()))
     result = script.pip_install_local(
         '-c', script.scratch_path / 'constraints.txt', to_install + '[baz]')
     assert 'Running setup.py install for LocalExtras' in result.stdout
@@ -492,11 +497,10 @@ def test_install_distribution_union_conflicting_extras(script, data):
 def test_install_unsupported_wheel_link_with_marker(script):
     script.scratch_path.joinpath("with-marker.txt").write_text(
         textwrap.dedent("""\
-            %s; %s
-        """) %
-        (
-            'https://github.com/a/b/c/asdf-1.5.2-cp27-none-xyz.whl',
-            'sys_platform == "xyz"'
+            {url}; {req}
+        """).format(
+            url='https://github.com/a/b/c/asdf-1.5.2-cp27-none-xyz.whl',
+            req='sys_platform == "xyz"',
         )
     )
     result = script.pip(
@@ -511,9 +515,10 @@ def test_install_unsupported_wheel_link_with_marker(script):
 def test_install_unsupported_wheel_file(script, data):
     # Trying to install a local wheel with an incompatible version/type
     # should fail.
+    path = data.packages.joinpath("simple.dist-0.1-py1-none-invalid.whl")
     script.scratch_path.joinpath("wheel-file.txt").write_text(textwrap.dedent("""\
-        %s
-        """ % data.packages.joinpath("simple.dist-0.1-py1-none-invalid.whl")))
+        {path}
+        """.format(**locals())))
     result = script.pip(
         'install', '-r', script.scratch_path / 'wheel-file.txt',
         expect_error=True,
@@ -538,9 +543,9 @@ def test_install_options_local_to_package(script, data):
     reqs_file = script.scratch_path.joinpath("reqs.txt")
     reqs_file.write_text(
         textwrap.dedent("""
-            simple --install-option='--home=%s'
+            simple --install-option='--home={home_simple}'
             INITools
-            """ % home_simple))
+            """.format(**locals())))
     result = script.pip(
         'install',
         '--no-index', '-f', data.find_links,
diff --git a/tests/functional/test_install_upgrade.py b/tests/functional/test_install_upgrade.py
index 0024de4d438..87ccd893afc 100644
--- a/tests/functional/test_install_upgrade.py
+++ b/tests/functional/test_install_upgrade.py
@@ -46,11 +46,13 @@ def test_only_if_needed_does_not_upgrade_deps_when_satisfied(script):
     )
 
     assert (
-        (script.site_packages / 'require_simple-1.0-py%s.egg-info' % pyversion)
+        (script.site_packages / 'require_simple-1.0-py{pyversion}.egg-info'
+            .format(**globals()))
         not in result.files_deleted
     ), "should have installed require_simple==1.0"
     assert (
-        (script.site_packages / 'simple-2.0-py%s.egg-info' % pyversion)
+        (script.site_packages / 'simple-2.0-py{pyversion}.egg-info'
+            .format(**globals()))
         not in result.files_deleted
     ), "should not have uninstalled simple==2.0"
     assert (
@@ -70,16 +72,23 @@ def test_only_if_needed_does_upgrade_deps_when_no_longer_satisfied(script):
     )
 
     assert (
-        (script.site_packages / 'require_simple-1.0-py%s.egg-info' % pyversion)
+        (script.site_packages / 'require_simple-1.0-py{pyversion}.egg-info'
+            .format(**globals()))
         not in result.files_deleted
     ), "should have installed require_simple==1.0"
+    expected = (
+        script.site_packages /
+        'simple-3.0-py{pyversion}.egg-info'.format(**globals())
+    )
     assert (
-        script.site_packages / 'simple-3.0-py%s.egg-info' %
-        pyversion in result.files_created
+        expected in result.files_created
     ), "should have installed simple==3.0"
+    expected = (
+        script.site_packages /
+        'simple-1.0-py{pyversion}.egg-info'.format(**globals())
+    )
     assert (
-        script.site_packages / 'simple-1.0-py%s.egg-info' %
-        pyversion in result.files_deleted
+        expected in result.files_deleted
     ), "should have uninstalled simple==1.0"
 
 
@@ -94,11 +103,13 @@ def test_eager_does_upgrade_dependecies_when_currently_satisfied(script):
     )
 
     assert (
-        (script.site_packages / 'require_simple-1.0-py%s.egg-info' % pyversion)
+        (script.site_packages /
+            'require_simple-1.0-py{pyversion}.egg-info'.format(**globals()))
         not in result.files_deleted
     ), "should have installed require_simple==1.0"
     assert (
-        (script.site_packages / 'simple-2.0-py%s.egg-info' % pyversion)
+        (script.site_packages /
+            'simple-2.0-py{pyversion}.egg-info'.format(**globals()))
         in result.files_deleted
     ), "should have uninstalled simple==2.0"
 
@@ -114,16 +125,19 @@ def test_eager_does_upgrade_dependecies_when_no_longer_satisfied(script):
     )
 
     assert (
-        (script.site_packages / 'require_simple-1.0-py%s.egg-info' % pyversion)
+        (script.site_packages /
+            'require_simple-1.0-py{pyversion}.egg-info'.format(**globals()))
         not in result.files_deleted
     ), "should have installed require_simple==1.0"
     assert (
-        script.site_packages / 'simple-3.0-py%s.egg-info' %
-        pyversion in result.files_created
+        script.site_packages /
+        'simple-3.0-py{pyversion}.egg-info'.format(**globals())
+        in result.files_created
     ), "should have installed simple==3.0"
     assert (
-        script.site_packages / 'simple-1.0-py%s.egg-info' %
-        pyversion in result.files_deleted
+        script.site_packages /
+        'simple-1.0-py{pyversion}.egg-info'.format(**globals())
+        in result.files_deleted
     ), "should have uninstalled simple==1.0"
 
 
@@ -139,12 +153,14 @@ def test_upgrade_to_specific_version(script):
         'pip install with specific version did not upgrade'
     )
     assert (
-        script.site_packages / 'INITools-0.1-py%s.egg-info' %
-        pyversion in result.files_deleted
+        script.site_packages / 'INITools-0.1-py{pyversion}.egg-info'
+        .format(**globals())
+        in result.files_deleted
     )
     assert (
-        script.site_packages / 'INITools-0.2-py%s.egg-info' %
-        pyversion in result.files_created
+        script.site_packages / 'INITools-0.2-py{pyversion}.egg-info'
+        .format(**globals())
+        in result.files_created
     )
 
 
@@ -158,8 +174,9 @@ def test_upgrade_if_requested(script):
     result = script.pip('install', '--upgrade', 'INITools')
     assert result.files_created, 'pip install --upgrade did not upgrade'
     assert (
-        script.site_packages / 'INITools-0.1-py%s.egg-info' %
-        pyversion not in result.files_created
+        script.site_packages /
+        'INITools-0.1-py{pyversion}.egg-info'.format(**globals())
+        not in result.files_created
     )
 
 
@@ -322,12 +339,14 @@ def test_should_not_install_always_from_cache(script):
     script.pip('uninstall', '-y', 'INITools')
     result = script.pip('install', 'INITools==0.1')
     assert (
-        script.site_packages / 'INITools-0.2-py%s.egg-info' %
-        pyversion not in result.files_created
+        script.site_packages /
+        'INITools-0.2-py{pyversion}.egg-info'.format(**globals())
+        not in result.files_created
     )
     assert (
-        script.site_packages / 'INITools-0.1-py%s.egg-info' %
-        pyversion in result.files_created
+        script.site_packages /
+        'INITools-0.1-py{pyversion}.egg-info'.format(**globals())
+        in result.files_created
     )
 
 
@@ -341,18 +360,22 @@ def test_install_with_ignoreinstalled_requested(script):
     assert result.files_created, 'pip install -I did not install'
     # both the old and new metadata should be present.
     assert os.path.exists(
-        script.site_packages_path / 'INITools-0.1-py%s.egg-info' % pyversion
+        script.site_packages_path /
+        'INITools-0.1-py{pyversion}.egg-info'.format(**globals())
     )
     assert os.path.exists(
-        script.site_packages_path / 'INITools-0.3-py%s.egg-info' % pyversion
+        script.site_packages_path /
+        'INITools-0.3-py{pyversion}.egg-info'.format(**globals())
     )
 
 
 @pytest.mark.network
 def test_upgrade_vcs_req_with_no_dists_found(script, tmpdir):
     """It can upgrade a VCS requirement that has no distributions otherwise."""
-    req = "%s#egg=pip-test-package" % local_checkout(
-        "git+https://github.com/pypa/pip-test-package.git", tmpdir,
+    req = "{checkout}#egg=pip-test-package".format(
+        checkout=local_checkout(
+            "git+https://github.com/pypa/pip-test-package.git", tmpdir,
+        )
     )
     script.pip("install", req)
     result = script.pip("install", "-U", req)
@@ -365,10 +388,11 @@ def test_upgrade_vcs_req_with_dist_found(script):
     # TODO(pnasrat) Using local_checkout fails on windows - oddness with the
     # test path urls/git.
     req = (
-        "%s#egg=pretend" %
-        (
-            "git+git://github.com/alex/pretend@e7f26ad7dbcb4a02a4995aade4"
-            "743aad47656b27"
+        "{url}#egg=pretend".format(
+            url=(
+                "git+git://github.com/alex/pretend@e7f26ad7dbcb4a02a4995aade4"
+                "743aad47656b27"
+            ),
         )
     )
     script.pip("install", req, expect_stderr=True)
@@ -401,7 +425,8 @@ class TestUpgradeDistributeToSetuptools(object):
 
     def prep_ve(self, script, version, pip_src, distribute=False):
         self.script = script
-        self.script.pip_install_local('virtualenv==%s' % version)
+        self.script.pip_install_local(
+            'virtualenv=={version}'.format(**locals()))
         args = ['virtualenv', self.script.scratch_path / 'VE']
         if distribute:
             args.insert(1, '--distribute')
diff --git a/tests/functional/test_install_user.py b/tests/functional/test_install_user.py
index 2cc91f56c75..8432dbc0bd6 100644
--- a/tests/functional/test_install_user.py
+++ b/tests/functional/test_install_user.py
@@ -52,8 +52,10 @@ def test_install_subversion_usersite_editable_with_distribute(
         """
         result = script.pip(
             'install', '--user', '-e',
-            '%s#egg=initools' %
-            local_checkout('svn+http://svn.colorstudy.com/INITools', tmpdir)
+            '{checkout}#egg=initools'.format(
+                checkout=local_checkout(
+                    'svn+http://svn.colorstudy.com/INITools', tmpdir)
+            )
         )
         result.assert_installed('INITools', use_user_site=True)
 
@@ -110,7 +112,7 @@ def test_install_user_conflict_in_usersite(self, script):
 
         # usersite has 0.1
         egg_info_folder = (
-            script.user_site / 'INITools-0.1-py%s.egg-info' % pyversion
+            script.user_site / 'INITools-0.1-py{pyversion}.egg-info'.format(**globals())
         )
         initools_v3_file = (
             # file only in 0.3
@@ -136,7 +138,7 @@ def test_install_user_conflict_in_globalsite(self, virtualenv, script):
 
         # usersite has 0.1
         egg_info_folder = (
-            script.user_site / 'INITools-0.1-py%s.egg-info' % pyversion
+            script.user_site / 'INITools-0.1-py{pyversion}.egg-info'.format(**globals())
         )
         initools_folder = script.user_site / 'initools'
         assert egg_info_folder in result2.files_created, str(result2)
@@ -145,7 +147,7 @@ def test_install_user_conflict_in_globalsite(self, virtualenv, script):
         # site still has 0.2 (can't look in result1; have to check)
         egg_info_folder = (
             script.base_path / script.site_packages /
-            'INITools-0.2-py%s.egg-info' % pyversion
+            'INITools-0.2-py{pyversion}.egg-info'.format(**globals())
         )
         initools_folder = script.base_path / script.site_packages / 'initools'
         assert isdir(egg_info_folder)
@@ -166,7 +168,7 @@ def test_upgrade_user_conflict_in_globalsite(self, virtualenv, script):
 
         # usersite has 0.3.1
         egg_info_folder = (
-            script.user_site / 'INITools-0.3.1-py%s.egg-info' % pyversion
+            script.user_site / 'INITools-0.3.1-py{pyversion}.egg-info'.format(**globals())
         )
         initools_folder = script.user_site / 'initools'
         assert egg_info_folder in result2.files_created, str(result2)
@@ -175,7 +177,7 @@ def test_upgrade_user_conflict_in_globalsite(self, virtualenv, script):
         # site still has 0.2 (can't look in result1; have to check)
         egg_info_folder = (
             script.base_path / script.site_packages /
-            'INITools-0.2-py%s.egg-info' % pyversion
+            'INITools-0.2-py{pyversion}.egg-info'.format(**globals())
         )
         initools_folder = script.base_path / script.site_packages / 'initools'
         assert isdir(egg_info_folder), result2.stdout
@@ -199,7 +201,7 @@ def test_install_user_conflict_in_globalsite_and_usersite(
 
         # usersite has 0.1
         egg_info_folder = (
-            script.user_site / 'INITools-0.1-py%s.egg-info' % pyversion
+            script.user_site / 'INITools-0.1-py{pyversion}.egg-info'.format(**globals())
         )
         initools_v3_file = (
             # file only in 0.3
@@ -212,7 +214,7 @@ def test_install_user_conflict_in_globalsite_and_usersite(
         # site still has 0.2 (can't just look in result1; have to check)
         egg_info_folder = (
             script.base_path / script.site_packages /
-            'INITools-0.2-py%s.egg-info' % pyversion
+            'INITools-0.2-py{pyversion}.egg-info'.format(**globals())
         )
         initools_folder = script.base_path / script.site_packages / 'initools'
         assert isdir(egg_info_folder)
@@ -241,6 +243,9 @@ def test_install_user_in_global_virtualenv_with_conflict_fails(
         dist_location = resultp.stdout.strip()
         assert (
             "Will not install to the user site because it will lack sys.path "
-            "precedence to %s in %s" %
-            ('INITools', dist_location) in result2.stderr
+            "precedence to {name} in {location}".format(
+                name='INITools',
+                location=dist_location,
+            )
+            in result2.stderr
         )
diff --git a/tests/functional/test_install_vcs_git.py b/tests/functional/test_install_vcs_git.py
index 01fec7a8bd4..3cb4d1490b2 100644
--- a/tests/functional/test_install_vcs_git.py
+++ b/tests/functional/test_install_vcs_git.py
@@ -171,7 +171,7 @@ def test_install_noneditable_git(script, tmpdir):
     )
     egg_info_folder = (
         script.site_packages /
-        'pip_test_package-0.1.1-py%s.egg-info' % pyversion
+        'pip_test_package-0.1.1-py{pyversion}.egg-info'.format(**globals())
     )
     result.assert_installed('piptestpackage',
                             without_egg_link=True,
diff --git a/tests/functional/test_pep517.py b/tests/functional/test_pep517.py
index d932f2ef83b..0286fe1f034 100644
--- a/tests/functional/test_pep517.py
+++ b/tests/functional/test_pep517.py
@@ -134,11 +134,13 @@ def test_conflicting_pep517_backend_requirements(script, tmpdir, data):
         project_dir,
         expect_error=True
     )
+    msg = (
+        'Some build dependencies for {url} conflict with the backend '
+        'dependencies: simplewheel==1.0 is incompatible with '
+        'simplewheel==2.0.'.format(url=path_to_url(project_dir)))
     assert (
         result.returncode != 0 and
-        ('Some build dependencies for %s conflict with the backend '
-         'dependencies: simplewheel==1.0 is incompatible with '
-         'simplewheel==2.0.' % path_to_url(project_dir)) in result.stderr
+        msg in result.stderr
     ), str(result)
 
 
diff --git a/tests/functional/test_uninstall.py b/tests/functional/test_uninstall.py
index e06ff024630..04d8550f32a 100644
--- a/tests/functional/test_uninstall.py
+++ b/tests/functional/test_uninstall.py
@@ -328,8 +328,9 @@ def test_uninstall_editable_from_svn(script, tmpdir):
     """
     result = script.pip(
         'install', '-e',
-        '%s#egg=initools' % (
-            local_checkout('svn+http://svn.colorstudy.com/INITools', tmpdir)
+        '{checkout}#egg=initools'.format(
+            checkout=local_checkout(
+                'svn+http://svn.colorstudy.com/INITools', tmpdir)
         ),
     )
     result.assert_installed('INITools')
@@ -396,10 +397,10 @@ def test_uninstall_from_reqs_file(script, tmpdir):
     )
     script.scratch_path.joinpath("test-req.txt").write_text(
         textwrap.dedent("""
-            -e %s#egg=initools
+            -e {url}#egg=initools
             # and something else to test out:
             PyLogo<0.4
-        """) % local_svn_url
+        """).format(url=local_svn_url)
     )
     result = script.pip('install', '-r', 'test-req.txt')
     script.scratch_path.joinpath("test-req.txt").write_text(
@@ -409,10 +410,10 @@ def test_uninstall_from_reqs_file(script, tmpdir):
             -i http://www.example.com
             --extra-index-url http://www.example.com
 
-            -e %s#egg=initools
+            -e {url}#egg=initools
             # and something else to test out:
             PyLogo<0.4
-        """) % local_svn_url
+        """).format(url=local_svn_url)
     )
     result2 = script.pip('uninstall', '-r', 'test-req.txt', '-y')
     assert_all_changes(
diff --git a/tests/functional/test_uninstall_user.py b/tests/functional/test_uninstall_user.py
index ed277739a1f..1b19294b78d 100644
--- a/tests/functional/test_uninstall_user.py
+++ b/tests/functional/test_uninstall_user.py
@@ -44,7 +44,7 @@ def test_uninstall_from_usersite_with_dist_in_global_site(
         # site still has 0.2 (can't look in result1; have to check)
         egg_info_folder = (
             script.base_path / script.site_packages /
-            'pip_test_package-0.1-py%s.egg-info' % pyversion
+            'pip_test_package-0.1-py{pyversion}.egg-info'.format(**globals())
         )
         assert isdir(egg_info_folder)
 
diff --git a/tests/functional/test_wheel.py b/tests/functional/test_wheel.py
index 181ca05845b..a5c156019e6 100644
--- a/tests/functional/test_wheel.py
+++ b/tests/functional/test_wheel.py
@@ -48,12 +48,12 @@ def test_pip_wheel_success(script, data):
         'wheel', '--no-index', '-f', data.find_links,
         'simple==3.0',
     )
-    wheel_file_name = 'simple-3.0-py%s-none-any.whl' % pyversion[0]
+    wheel_file_name = 'simple-3.0-py{pyversion[0]}-none-any.whl'.format(**globals())
     wheel_file_path = script.scratch / wheel_file_name
     assert re.search(
         r"Created wheel for simple: "
-        r"filename=%s size=\d+ sha256=[A-Fa-f0-9]{64}"
-        % re.escape(wheel_file_name), result.stdout)
+        r"filename={filename} size=\d+ sha256=[A-Fa-f0-9]{64}"
+        .format(filename=re.escape(wheel_file_name)), result.stdout)
     assert re.search(
         r"^\s+Stored in directory: ", result.stdout, re.M)
     assert wheel_file_path in result.files_created, result.stdout
@@ -68,7 +68,7 @@ def test_pip_wheel_build_cache(script, data):
         'wheel', '--no-index', '-f', data.find_links,
         'simple==3.0',
     )
-    wheel_file_name = 'simple-3.0-py%s-none-any.whl' % pyversion[0]
+    wheel_file_name = 'simple-3.0-py{pyversion[0]}-none-any.whl'.format(**globals())
     wheel_file_path = script.scratch / wheel_file_name
     assert wheel_file_path in result.files_created, result.stdout
     assert "Successfully built simple" in result.stdout, result.stdout
@@ -145,7 +145,7 @@ def test_pip_wheel_builds_editable_deps(script, data):
         'wheel', '--no-index', '-f', data.find_links,
         '-e', editable_path
     )
-    wheel_file_name = 'simple-1.0-py%s-none-any.whl' % pyversion[0]
+    wheel_file_name = 'simple-1.0-py{pyversion[0]}-none-any.whl'.format(**globals())
     wheel_file_path = script.scratch / wheel_file_name
     assert wheel_file_path in result.files_created, result.stdout
 
@@ -159,7 +159,7 @@ def test_pip_wheel_builds_editable(script, data):
         'wheel', '--no-index', '-f', data.find_links,
         '-e', editable_path
     )
-    wheel_file_name = 'simplewheel-1.0-py%s-none-any.whl' % pyversion[0]
+    wheel_file_name = 'simplewheel-1.0-py{pyversion[0]}-none-any.whl'.format(**globals())
     wheel_file_path = script.scratch / wheel_file_name
     assert wheel_file_path in result.files_created, result.stdout
 
@@ -173,7 +173,7 @@ def test_pip_wheel_fail(script, data):
         'wheelbroken==0.1',
         expect_error=True,
     )
-    wheel_file_name = 'wheelbroken-0.1-py%s-none-any.whl' % pyversion[0]
+    wheel_file_name = 'wheelbroken-0.1-py{pyversion[0]}-none-any.whl'.format(**globals())
     wheel_file_path = script.scratch / wheel_file_name
     assert wheel_file_path not in result.files_created, (
         wheel_file_path,
@@ -191,12 +191,12 @@ def test_no_clean_option_blocks_cleaning_after_wheel(script, data):
     build = script.venv_path / 'build'
     result = script.pip(
         'wheel', '--no-clean', '--no-index', '--build', build,
-        '--find-links=%s' % data.find_links,
+        '--find-links={data.find_links}'.format(**locals()),
         'simple',
         expect_temp=True,
     )
     build = build / 'simple'
-    assert exists(build), "build/simple should still exist %s" % str(result)
+    assert exists(build), "build/simple should still exist {result}".format(**locals())
 
 
 def test_pip_wheel_source_deps(script, data):
@@ -209,7 +209,7 @@ def test_pip_wheel_source_deps(script, data):
         'wheel', '--no-index', '-f', data.find_links,
         'requires_source',
     )
-    wheel_file_name = 'source-1.0-py%s-none-any.whl' % pyversion[0]
+    wheel_file_name = 'source-1.0-py{pyversion[0]}-none-any.whl'.format(**globals())
     wheel_file_path = script.scratch / wheel_file_name
     assert wheel_file_path in result.files_created, result.stdout
     assert "Successfully built source" in result.stdout, result.stdout
@@ -228,7 +228,7 @@ def test_pip_wheel_fail_cause_of_previous_build_dir(script, data):
 
     # When I call pip trying to install things again
     result = script.pip(
-        'wheel', '--no-index', '--find-links=%s' % data.find_links,
+        'wheel', '--no-index', '--find-links={data.find_links}'.format(**locals()),
         '--build', script.venv_path / 'build',
         'simple==3.0', expect_error=True, expect_temp=True,
     )
@@ -248,7 +248,7 @@ def test_wheel_package_with_latin1_setup(script, data):
 def test_pip_wheel_with_pep518_build_reqs(script, data, common_wheels):
     result = script.pip('wheel', '--no-index', '-f', data.find_links,
                         '-f', common_wheels, 'pep518==3.0',)
-    wheel_file_name = 'pep518-3.0-py%s-none-any.whl' % pyversion[0]
+    wheel_file_name = 'pep518-3.0-py{pyversion[0]}-none-any.whl'.format(**globals())
     wheel_file_path = script.scratch / wheel_file_name
     assert wheel_file_path in result.files_created, result.stdout
     assert "Successfully built pep518" in result.stdout, result.stdout
@@ -261,7 +261,7 @@ def test_pip_wheel_with_pep518_build_reqs_no_isolation(script, data):
         'wheel', '--no-index', '-f', data.find_links,
         '--no-build-isolation', 'pep518==3.0',
     )
-    wheel_file_name = 'pep518-3.0-py%s-none-any.whl' % pyversion[0]
+    wheel_file_name = 'pep518-3.0-py{pyversion[0]}-none-any.whl'.format(**globals())
     wheel_file_path = script.scratch / wheel_file_name
     assert wheel_file_path in result.files_created, result.stdout
     assert "Successfully built pep518" in result.stdout, result.stdout
@@ -289,7 +289,7 @@ def test_pep517_wheels_are_not_confused_with_other_files(script, tmpdir, data):
     result = script.pip('wheel', pkg_to_wheel, '-w', script.scratch_path)
     assert "Installing build dependencies" in result.stdout, result.stdout
 
-    wheel_file_name = 'withpyproject-0.0.1-py%s-none-any.whl' % pyversion[0]
+    wheel_file_name = 'withpyproject-0.0.1-py{pyversion[0]}-none-any.whl'.format(**globals())
     wheel_file_path = script.scratch / wheel_file_name
     assert wheel_file_path in result.files_created, result.stdout
 
@@ -303,6 +303,6 @@ def test_legacy_wheels_are_not_confused_with_other_files(script, tmpdir, data):
     result = script.pip('wheel', pkg_to_wheel, '-w', script.scratch_path)
     assert "Installing build dependencies" not in result.stdout, result.stdout
 
-    wheel_file_name = 'simplewheel-1.0-py%s-none-any.whl' % pyversion[0]
+    wheel_file_name = 'simplewheel-1.0-py{pyversion[0]}-none-any.whl'.format(**globals())
     wheel_file_path = script.scratch / wheel_file_name
     assert wheel_file_path in result.files_created, result.stdout
diff --git a/tests/lib/__init__.py b/tests/lib/__init__.py
index c0baa0a1cfb..7bece427099 100644
--- a/tests/lib/__init__.py
+++ b/tests/lib/__init__.py
@@ -285,14 +285,16 @@ def assert_installed(self, pkg_name, editable=True, with_files=[],
         if without_egg_link:
             if egg_link_path in self.files_created:
                 raise TestFailure(
-                    'unexpected egg link file created: %r\n%s' %
-                    (egg_link_path, self)
+                    'unexpected egg link file created: '
+                    '{egg_link_path!r}\n{self}'
+                    .format(**locals())
                 )
         else:
             if egg_link_path not in self.files_created:
                 raise TestFailure(
-                    'expected egg link file missing: %r\n%s' %
-                    (egg_link_path, self)
+                    'expected egg link file missing: '
+                    '{egg_link_path!r}\n{self}'
+                    .format(**locals())
                 )
 
             egg_link_file = self.files_created[egg_link_path]
@@ -301,15 +303,15 @@ def assert_installed(self, pkg_name, editable=True, with_files=[],
             # FIXME: I don't understand why there's a trailing . here
             if not (egg_link_contents.endswith('\n.') and
                     egg_link_contents[:-2].endswith(pkg_dir)):
-                raise TestFailure(textwrap.dedent(u'''\
-                    Incorrect egg_link file %r
-                    Expected ending: %r
+                raise TestFailure(textwrap.dedent(
+                    u'''\
+                    Incorrect egg_link file {egg_link_file!r}
+                    Expected ending: {expected_ending!r}
                     ------- Actual contents -------
-                    %s
-                    -------------------------------''' % (
-                    egg_link_file,
-                    pkg_dir + '\n.',
-                    repr(egg_link_contents))
+                    {egg_link_contents!r}
+                    -------------------------------'''.format(
+                        expected_ending=pkg_dir + '\n.',
+                        **locals())
                 ))
 
         if use_user_site:
@@ -318,8 +320,10 @@ def assert_installed(self, pkg_name, editable=True, with_files=[],
             pth_file = e.site_packages / 'easy-install.pth'
 
         if (pth_file in self.files_updated) == without_egg_link:
-            raise TestFailure('%r unexpectedly %supdated by install' % (
-                pth_file, (not without_egg_link and 'not ' or '')))
+            raise TestFailure(
+                '{pth_file} unexpectedly {maybe}updated by install'.format(
+                    maybe=not without_egg_link and 'not ' or '',
+                    **locals()))
 
         if (pkg_dir in self.files_created) == (curdir in without_files):
             raise TestFailure(textwrap.dedent('''\