Fix how docs gets pip version, to work around an issue with readthedocs

docs/conf.py

@@ -12,6 +12,7 @@
 # serve to show the default.
 
 import os
+import re
 import sys
 import glob
 
@@ -59,14 +60,27 @@ copyright = '2008-2017, PyPA'
 # built documents.
 #
 # The short X.Y version.
-try:
-    from pip import __version__
-    # The short X.Y version.
-    version = '.'.join(__version__.split('.')[:2])
-    # The full version, including alpha/beta/rc tags.
-    release = __version__
-except ImportError:
-    version = release = 'dev'
+
+version = release = 'dev'
+
+# Readthedocs seems to install pip as an egg (via setup.py install) which
+# is somehow resulting in "import pip" picking up an older copy of pip.
+# Rather than trying to force RTD to install pip properly, we'll simply
+# read the version direct from the __init__.py file. (Yes, this is
+# fragile, but it works...)
+root = os.path.dirname(os.path.dirname(__file__))
+pip_init = os.path.join(root, 'src', 'pip', '__init__.py')
+
+with open(pip_init, encoding='utf-8') as f:
+    for line in f:
+        m = re.match(r'__version__ = "(.*)"', line)
+        if m:
+            __version__ = m.group(1)
+            # The short X.Y version.
+            version = '.'.join(__version__.split('.')[:2])
+            # The full version, including alpha/beta/rc tags.
+            release = __version__
+            break
 
 # We have this here because readthedocs plays tricks sometimes and there seems
 # to be a hiesenbug, related to the version of pip discovered. This is here to