diff --git a/.travis.yml b/.travis.yml
index 375d8bb..8a30d01 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -7,19 +7,14 @@ arch:
   - ppc64le
   - arm64
 python:
-  - '2.7'
-  - '3.4'
-  - '3.5'
-  - '3.6'
-  - '3.7'
   - '3.8'
   - '3.9'
   - '3.10'
+  - '3.11'
   - pypy
 
 matrix:
   exclude:
-    - python: 3.4
     - arch: ppc64le
       python: pypy
     - arch: arm64
@@ -32,9 +27,10 @@ env:
 - DEPEENDENCIES="flask==0.10 werkzeug==0.16.1"
 - DEPEENDENCIES="flask==1.0"
 - DEPEENDENCIES="flask==1.1"
+- DEPEENDENCIES="flask==2.3.2"
 
 install:
-  - pip install -U setuptools pep8 six coverage docutils pygments packaging $DEPEENDENCIES
+  - pip install -U setuptools pep8 coverage docutils pygments packaging $DEPEENDENCIES
 
 script:
   - coverage erase
diff --git a/README.rst b/README.rst
index 347a67c..f90ac6c 100644
--- a/README.rst
+++ b/README.rst
@@ -97,6 +97,9 @@ Tests
 A simple set of tests is included in ``test/``. 
 To run, install nose, and simply invoke ``nosetests`` or ``python setup.py test`` to exercise the tests.
 
+If nosetests does not work for you, due to it no longer working with newer python versions.
+You can use pytest to run the tests instead.
+
 Contributing
 ------------
 
diff --git a/flask_cors/__init__.py b/flask_cors/__init__.py
index c84a763..458150e 100644
--- a/flask_cors/__init__.py
+++ b/flask_cors/__init__.py
@@ -24,4 +24,4 @@
 rootlogger.addHandler(NullHandler())
 
 if rootlogger.level == logging.NOTSET:
-    rootlogger.setLevel(logging.WARN)
\ No newline at end of file
+    rootlogger.setLevel(logging.WARN)
diff --git a/flask_cors/core.py b/flask_cors/core.py
index 6079064..5358036 100644
--- a/flask_cors/core.py
+++ b/flask_cors/core.py
@@ -9,14 +9,8 @@
 """
 import re
 import logging
-try:
-    # on python 3
-    from collections.abc import Iterable
-except ImportError:
-    # on python 2.7 and pypy
-    from collections import Iterable
+from collections.abc import Iterable
 from datetime import timedelta
-from six import string_types
 from flask import request, current_app
 from werkzeug.datastructures import Headers, MultiDict
 
@@ -82,7 +76,7 @@ def pattern_length(pair):
                       key=pattern_length,
                       reverse=True)
 
-    elif isinstance(resources, string_types):
+    elif isinstance(resources, str):
         return [(re_fix(resources), {})]
 
     elif isinstance(resources, Iterable):
@@ -329,9 +323,8 @@ def flexible_str(obj):
     """
     if obj is None:
         return None
-    elif(not isinstance(obj, string_types)
-            and isinstance(obj, Iterable)):
-        return ', '.join(str(item) for item in sorted(obj))
+    elif not isinstance(obj, str) and isinstance(obj, Iterable):
+        return ", ".join(str(item) for item in sorted(obj))
     else:
         return str(obj)
 
@@ -346,7 +339,7 @@ def ensure_iterable(inst):
     """
     Wraps scalars or string types as a list, or returns the iterable instance.
     """
-    if isinstance(inst, string_types):
+    if isinstance(inst, str):
         return [inst]
     elif not isinstance(inst, Iterable):
         return [inst]
diff --git a/flask_cors/decorator.py b/flask_cors/decorator.py
index 2c7a28e..b61d22f 100644
--- a/flask_cors/decorator.py
+++ b/flask_cors/decorator.py
@@ -9,9 +9,11 @@
     :copyright: (c) 2016 by Cory Dolphin.
     :license: MIT, see LICENSE for more details.
 """
+import logging
 from functools import update_wrapper
 from flask import make_response, request, current_app
-from .core import *
+
+from .core import get_cors_options, set_cors_headers, FLASK_CORS_EVALUATED
 
 LOG = logging.getLogger(__name__)
 
diff --git a/flask_cors/extension.py b/flask_cors/extension.py
index 7695aad..1d2d938 100644
--- a/flask_cors/extension.py
+++ b/flask_cors/extension.py
@@ -8,12 +8,19 @@
     :copyright: (c) 2016 by Cory Dolphin.
     :license: MIT, see LICENSE for more details.
 """
+import logging
+from urllib.parse import unquote_plus
 from flask import request
-from .core import *
-try:
-    from urllib.parse import unquote_plus
-except ImportError:
-    from urllib import unquote_plus
+
+from .core import (
+    parse_resources,
+    get_cors_options,
+    get_regexp_pattern,
+    ACL_ORIGIN,
+    try_match,
+    set_cors_headers
+)
+
 
 LOG = logging.getLogger(__name__)
 
diff --git a/flask_cors/version.py b/flask_cors/version.py
index dd25542..d6497a8 100644
--- a/flask_cors/version.py
+++ b/flask_cors/version.py
@@ -1 +1 @@
-__version__ = '3.1.01'
+__version__ = '4.0.0'
diff --git a/requirements.txt b/requirements.txt
index 4d6ccbc..af05533 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,2 +1 @@
 Flask>=0.9
-Six
diff --git a/setup.py b/setup.py
index 91a26d6..b10bd39 100644
--- a/setup.py
+++ b/setup.py
@@ -43,16 +43,10 @@
         'License :: OSI Approved :: MIT License',
         'Operating System :: OS Independent',
         'Programming Language :: Python',
-        'Programming Language :: Python :: 2',
-        'Programming Language :: Python :: 2.7',
-        'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.4',
-        'Programming Language :: Python :: 3.5',
-        'Programming Language :: Python :: 3.6',
-        'Programming Language :: Python :: 3.7',
         'Programming Language :: Python :: 3.8',
         'Programming Language :: Python :: 3.9',
         'Programming Language :: Python :: 3.10',
+        'Programming Language :: Python :: 3.11',
         'Programming Language :: Python :: Implementation :: CPython',
         'Programming Language :: Python :: Implementation :: PyPy',
         'Topic :: Internet :: WWW/HTTP :: Dynamic Content',