use pip to install dependencies first

- to avoid having to run `setup.py` twice manually, which can go unnoticed if this package is being installed as a dependency.
- because `setup_requires` only downloads packages, w/o installing them
- because the combination of `setup_requires` with `install_requires` do not work as expected under all circumstances [1].
- even if they did work as desired, some intermediate callback would have to be passed to `setuptools.setup`, to be called between `setup_requires` and what follows. This approach is nested, thus against PEP 20.
- so better flat, i.e., first install the necessary dependencies, then build the parser table, then call `setuptools.setup`
- requires that `pip` be present, but not having `pip` is a bad idea anyway -- avoid using `easy_install` (which is available as `setuptools.command.easy_install`)
- a branch tarball is downloaded from github to avoid cloning the whole repository, which is what `pip` does if given a git repo
- so using `pip` isn't strictly necessary, but if we did fetch from a repo, it would be necessary, because that's not possible with vanilla `setuptools`.
- it also simplifies code by not having to try-except, just let `pip` skip dependencies that are already met.
- if the table generation fails for some reason other than absence of `ply`, that will not go unnoticed any more.

[1] https://bitbucket.org/pypa/setuptools/issue/209/setup_requires-and-install_requires-dont

setup.py

@@ -1,3 +1,4 @@
+import pip
 from setuptools import setup
 
 
@@ -15,19 +16,22 @@
     "version = '{version}'\n").format(version=version)
 
 
+def build_parser_table():
+    from promela import yacc
+    tabmodule = yacc.TABMODULE.split('.')[-1]
+    outputdir = 'promela/'
+    parser = yacc.Parser()
+    parser.build(tabmodule, outputdir=outputdir, write_tables=True)
+
+
 if __name__ == '__main__':
+    pip.main(['install', 'ply == 3.4'])
+    pip.main(['install',
+              '--allow-unverified', 'networkx>=2.0dev',
+              'https://github.com/networkx/networkx/archive/master.zip'])
+    build_parser_table()
     with open(VERSION_FILE, 'w') as f:
         f.write(s)
-    # build parser table
-    try:
-        from promela import yacc
-        tabmodule = yacc.TABMODULE.split('.')[-1]
-        outputdir = 'promela/'
-        parser = yacc.Parser()
-        parser.build(tabmodule, outputdir=outputdir, write_tables=True)
-        plytable_build_failed = False
-    except AssertionError:
-        plytable_build_failed = True
     setup(
         name='promela',
         version=version,
@@ -42,7 +46,3 @@
         tests_require=['nose'],
         packages=['promela'],
         package_dir={'promela': 'promela'})
-    if plytable_build_failed:
-        print(
-            'ERROR: failed to build parser table.'
-            'Please run setup.py again.')