Issue #23703: Fix a regression in urljoin() introduced in 901e4e52b20a.

Patch by Demian Brecht.

Lib/test/test_urlparse.py

@@ -391,6 +391,9 @@ class UrlParseTestCase(unittest.TestCase):
         self.checkJoin('http://a/b/c/d/e/', '../../f/g', 'http://a/b/c/f/g')
         self.checkJoin('http://a/b/', '../../f/g/', 'http://a/f/g/')
 
+        # issue 23703: don't duplicate filename
+        self.checkJoin('a', 'b', 'b')
+
     def test_RFC2732(self):
         str_cases = [
             ('http://Test.python.org:5432/foo/', 'test.python.org', 5432),

Lib/urllib/parse.py

@@ -447,8 +447,7 @@ def urljoin(base, url, allow_fragments=True):
         segments = base_parts + path.split('/')
         # filter out elements that would cause redundant slashes on re-joining
         # the resolved_path
-        segments = segments[0:1] + [
-            s for s in segments[1:-1] if len(s) > 0] + segments[-1:]
+        segments[1:-1] = filter(None, segments[1:-1])
 
     resolved_path = []
 

Misc/NEWS

@@ -36,6 +36,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #23703: Fix a regression in urljoin() introduced in 901e4e52b20a.
+  Patch by Demian Brecht.
+
 - Issue #4254: Adds _curses.update_lines_cols() Patch by Arnon Yaari
 
 - Issue 19933: Provide default argument for ndigits in round. Patch by