Add relative_path method, with tests.

1 files changed, 25 insertions, 0 deletions

diff --git a/summainlib.py b/summainlib.py
index 7f67908..6628ce0 100644
--- a/summainlib.py
+++ b/summainlib.py
@@ -141,7 +141,32 @@ class FilesystemObject(object):
         
     def __getitem__(self, key):
         return self.values.get(key, '')
+
+    def _isdir(self):
+        '''Is this a directory?'''
+        
+        return stat.S_ISDIR(int(self['Mode'], 8))
+
+    def relative_path(self, root):
+        '''Return a path that is relative to root, if possible.
+        
+        If pathname does not start with root, then return it
+        unmodified.
         
+        '''
+        
+        if root.endswith(os.sep):
+            root2 = root
+        else:
+            root2 = root + os.sep
+        pathname = self['Name']
+        if pathname.startswith(root2):
+            return pathname[len(root2):]
+        elif pathname == root and self._isdir():
+            return '.'
+        else:
+            return pathname
+
     def format(self): # pragma: no cover
         keys = ['Name'] + [x 
                            for x in sorted(self.values.keys())