gh-117607: Speedup os.path.relpath() (GH-117608)

1 files changed, 5 insertions, 3 deletions

diff --git a/Lib/posixpath.py b/Lib/posixpath.py
index 56b7915..f189c33 100644
--- a/Lib/posixpath.py
+++ b/Lib/posixpath.py
@@ -532,15 +532,17 @@ def relpath(path, start=None):
         start = os.fspath(start)
 
     try:
-        start_list = [x for x in abspath(start).split(sep) if x]
-        path_list = [x for x in abspath(path).split(sep) if x]
+        start_tail = abspath(start).lstrip(sep)
+        path_tail = abspath(path).lstrip(sep)
+        start_list = start_tail.split(sep) if start_tail else []
+        path_list = path_tail.split(sep) if path_tail else []
         # 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)
+        return sep.join(rel_list)
     except (TypeError, AttributeError, BytesWarning, DeprecationWarning):
         genericpath._check_arg_types('relpath', path, start)
         raise