Add os.path.relpath function in logical.common.compat for pre-2.6 python.

1 files changed, 23 insertions, 0 deletions

diff --git a/compat.py b/compat.py
index ad0e63a..81ce4c7 100644
--- a/compat.py
+++ b/compat.py
@@ -286,3 +286,26 @@ except ImportError:
         if retcode:
             raise CalledProcessError(retcode, cmd)
         return retcode
+
+try:
+    from os.path import relpath
+except ImportError: # python < 2.6
+    from os.path import curdir, abspath, sep, commonprefix, pardir, join
+    def relpath(path, start=curdir):
+        """Return a relative version of a path"""
+
+        if not path:
+            raise ValueError("no path specified")
+
+        start_list = abspath(start).split(sep)
+        path_list = abspath(path).split(sep)
+
+        # Work out how much of the filepath is shared by start and path.
+        i = len(commonprefix([start_list, path_list]))
+
+        rel_list = [pardir] * (len(start_list)-i) + path_list[i:]
+        if not rel_list:
+            return curdir
+        return join(*rel_list)
+
+