#1742: don't raise exception on os.path.relpath("a", "a"), but return os.curdir.

Reported by Jesse Towner.

Lib/ntpath.py

@@ -490,4 +490,6 @@ def relpath(path, start=curdir):
         i += 1
 
     rel_list = [pardir] * (len(start_list)-i) + path_list[i:]
+    if not rel_list:
+        return curdir
     return join(*rel_list)

Lib/posixpath.py

@@ -398,4 +398,6 @@ def relpath(path, start=curdir):
     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)

Lib/test/test_ntpath.py

@@ -166,6 +166,7 @@ tester('ntpath.relpath("a", "../b")', '..\\'+currentdir+'\\a')
 tester('ntpath.relpath("a/b", "../c")', '..\\'+currentdir+'\\a\\b')
 tester('ntpath.relpath("a", "b/c")', '..\\..\\a')
 tester('ntpath.relpath("//conky/mountpoint/a", "//conky/mountpoint/b/c")', '..\\..\\a')
+tester('ntpath.relpath("a", "a")', '.')
 
 if errors:
     raise TestFailed(str(errors) + " errors.")

Lib/test/test_posixpath.py

@@ -501,6 +501,7 @@ class PosixPathTest(unittest.TestCase):
             self.assertEqual(posixpath.relpath("a", "../b"), "../"+curdir+"/a")
             self.assertEqual(posixpath.relpath("a/b", "../c"), "../"+curdir+"/a/b")
             self.assertEqual(posixpath.relpath("a", "b/c"), "../../a")
+            self.assertEqual(posixpath.relpath("a", "a"), ".")
         finally:
             os.getcwd = real_getcwd
 

Misc/NEWS

@@ -342,6 +342,9 @@ Core and builtins
 Library
 -------
 
+- Bug #1742: return os.curdir from os.path.relpath() if both arguments are
+  equal instead of raising an exception.
+
 - Patch #1637: fix urlparse for URLs like 'http://x.com?arg=/foo'.
 
 - Patch #1698: allow '@' in username parsed by urlparse.py.