Add compatibility layer for Python 2.6

os.path.relpath on Python 2.6 returns slightly different output than it
does on 2.7. Rather than try to write tests around the behaviour, it
makes sense to have a common relpath function that behaves the same on
every version.

flake8/compat.py

@@ -0,0 +1,12 @@
+# -*- coding: utf-8 -*-
+"""Compatibility shims for Flake8."""
+import os.path
+import sys
+
+
+def relpath(path, start='.'):
+    """Wallpaper over the differences between 2.6 and newer versions."""
+    if sys.version_info < (2, 7) and path.startswith(start):
+        return path[len(start):]
+    else:
+        return os.path.relpath(path, start=start)

flake8/hooks.py

@@ -12,6 +12,7 @@ try:
 except ImportError:   # Python 2
     from ConfigParser import ConfigParser
 
+from flake8 import compat
 from flake8.engine import get_parser, get_style_guide
 from flake8.main import DEFAULT_CONFIG
 
@@ -65,7 +66,7 @@ def git_hook(complexity=-1, strict=False, ignore=None, lazy=False):
             # avoid overwriting files with the same name
             dirname, filename = os.path.split(os.path.abspath(file_))
             prefix = os.path.commonprefix([dirname, tmpdir])
-            dirname = os.path.relpath(dirname, start=prefix)
+            dirname = compat.relpath(dirname, start=prefix)
             dirname = os.path.join(tmpdir, dirname)
             if not os.path.isdir(dirname):
                 os.makedirs(dirname)

flake8/tests/test_hooks.py

@@ -35,3 +35,7 @@ class TestGitHook(unittest.TestCase):
         tmpdir = os.path.join('/fake/tmp', dirname[1:])
         tmpfile = os.path.join(tmpdir, 'bfile.py')
         style_guide.check_files.assert_called_once_with([tmpfile])
+
+
+if __name__ == '__main__':
+    unittest.main()