Merge issue #26355 fix from Python 3.5

1 files changed, 6 insertions, 0 deletions

diff --git a/Lib/genericpath.py b/Lib/genericpath.py
index 671406197a..303b3b349a 100644
--- a/Lib/genericpath.py
+++ b/Lib/genericpath.py
@@ -69,6 +69,12 @@ def getctime(filename):
 def commonprefix(m):
     "Given a list of pathnames, returns the longest common leading component"
     if not m: return ''
+    # Some people pass in a list of pathname parts to operate in an OS-agnostic
+    # fashion; don't try to translate in that case as that's an abuse of the
+    # API and they are already doing what they need to be OS-agnostic and so
+    # they most likely won't be using an os.PathLike object in the sublists.
+    if not isinstance(m[0], (list, tuple)):
+        m = tuple(map(os.fspath, m))
     s1 = min(m)
     s2 = max(m)
     for i, c in enumerate(s1):