Single source the version number

Version number mismatches are annoying and it happened already twice in two years.
The pypi people have some solutions for that problem: https://packaging.python.org/single_source_version/

Now, the version is only defined at a single place; the __init__.py file in the pygccxml package.

Author: iMichka

docs/conf.py

@@ -21,6 +21,8 @@
 # documentation root, use os.path.abspath to make it absolute, like shown here.
 sys.path.insert(0, os.path.abspath('.') + "/../")
 
+from ..release_utils import utils  # nopep8
+
 # -- General configuration ------------------------------------------------
 
 # If your documentation needs a minimal Sphinx version, state it here.
@@ -55,9 +57,9 @@
 # built documents.
 #
 # The short X.Y version.
-version = '1.8.2'
+version = utils.find_version("../pygccxml/__init__.py")
 # The full version, including alpha/beta/rc tags.
-release = '1.8.2'
+release = utils.find_version("../pygccxml/__init__.py")
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.

release_utils/__init__.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python
+# Copyright 2014-2016 Insight Software Consortium.
+# Copyright 2004-2008 Roman Yakovenko.
+# Distributed under the Boost Software License, Version 1.0.
+# See http://www.boost.org/LICENSE_1_0.txt
+
+import io
+import os
+import re
+
+
+def find_version(file_path):
+    """
+    Find the version of pygccxml.
+
+    Used by setup.py and the sphinx's conf.py.
+    Inspired by https://packaging.python.org/single_source_version/
+
+    Args:
+        file_path (str): path to the file containing the version.
+    """
+
+    with io.open(
+            os.path.join(
+                os.path.dirname(__file__),
+                os.path.normpath(file_path)),
+            encoding="utf8") as fp:
+        content = fp.read()
+
+    version_match = re.search(r"^__version__ = ['\"]([^'\"]*)['\"]",
+                              content, re.M)
+    if version_match:
+        return version_match.group(1)
+    raise RuntimeError("Unable to find version string.")

release_utils/utils.py

@@ -5,16 +5,20 @@
 # See http://www.boost.org/LICENSE_1_0.txt
 
 from setuptools import setup
+from release_utils import utils
+
+version = utils.find_version("pygccxml/__init__.py")
 
 setup(name="pygccxml",
-      version="1.8.2",
+      version=version,
       author="Roman Yakovenko",
       author_email="roman yakovenko at gmail com",
       maintainer="Michka Popoff and the Insight Software Consortium",
       maintainer_email="[email protected]",
       description="Python package for easy C++ declarations navigation.",
       url="https://github.com/gccxml/pygccxml",
-      download_url="https://github.com/gccxml/pygccxml/archive/v1.8.1.tar.gz",
+      download_url="https://github.com/gccxml/pygccxml/archive/v" +
+                   version + ".tar.gz",
       license="Boost",
       keywords="C++, declaration parser, CastXML, gccxml",
       packages=["pygccxml",