[3.8] bpo-39667: Sync zipp 3.0 (GH-18540)

Doc/library/zipfile.rst

@@ -494,6 +494,12 @@ Path objects are traversable using the ``/`` operator.
    Invoke :meth:`ZipFile.open` on the current path. Accepts
    the same arguments as :meth:`ZipFile.open`.
 
+   .. caution::
+
+      The signature on this function changes in an incompatible way
+      in Python 3.9. For a future-compatible version, consider using
+      the third-party zipp.Path package (3.0 or later).
+
 .. method:: Path.iterdir()
 
    Enumerate the children of the current directory.

Lib/test/test_zipfile.py

@@ -5,6 +5,7 @@
 import os
 import pathlib
 import posixpath
+import string
 import struct
 import subprocess
 import sys
@@ -2933,6 +2934,11 @@ def test_joinpath_constant_time(self):
         # Check the file iterated all items
         assert entries.count == self.HUGE_ZIPFILE_NUM_ENTRIES
 
+    # @func_timeout.func_set_timeout(3)
+    def test_implied_dirs_performance(self):
+        data = ['/'.join(string.ascii_lowercase + str(n)) for n in range(10000)]
+        zipfile.CompleteDirs._implied_dirs(data)
+
 
 if __name__ == "__main__":
     unittest.main()

Lib/zipfile.py

@@ -17,7 +17,6 @@
 import threading
 import time
 import contextlib
-from collections import OrderedDict
 
 try:
     import zlib # We may need its compression method
@@ -2125,24 +2124,6 @@ def _compile(file, optimize=-1):
         return (fname, archivename)
 
 
-def _unique_everseen(iterable, key=None):
-    "List unique elements, preserving order. Remember all elements ever seen."
-    # unique_everseen('AAAABBBCCDAABBB') --> A B C D
-    # unique_everseen('ABBCcAD', str.lower) --> A B C D
-    seen = set()
-    seen_add = seen.add
-    if key is None:
-        for element in itertools.filterfalse(seen.__contains__, iterable):
-            seen_add(element)
-            yield element
-    else:
-        for element in iterable:
-            k = key(element)
-            if k not in seen:
-                seen_add(k)
-                yield element
-
-
 def _parents(path):
     """
     Given a path with elements separated by
@@ -2184,6 +2165,18 @@ def _ancestry(path):
         path, tail = posixpath.split(path)
 
 
+_dedupe = dict.fromkeys
+"""Deduplicate an iterable in original order"""
+
+
+def _difference(minuend, subtrahend):
+    """
+    Return items in minuend not in subtrahend, retaining order
+    with O(1) lookup.
+    """
+    return itertools.filterfalse(set(subtrahend).__contains__, minuend)
+
+
 class CompleteDirs(ZipFile):
     """
     A ZipFile subclass that ensures that implied directories
@@ -2193,13 +2186,8 @@ class CompleteDirs(ZipFile):
     @staticmethod
     def _implied_dirs(names):
         parents = itertools.chain.from_iterable(map(_parents, names))
-        # Deduplicate entries in original order
-        implied_dirs = OrderedDict.fromkeys(
-            p + posixpath.sep for p in parents
-            # Cast names to a set for O(1) lookups
-            if p + posixpath.sep not in set(names)
-        )
-        return implied_dirs
+        as_dirs = (p + posixpath.sep for p in parents)
+        return _dedupe(_difference(as_dirs, names))
 
     def namelist(self):
         names = super(CompleteDirs, self).namelist()

Misc/NEWS.d/next/Library/2020-02-17-22-38-15.bpo-39667.QuzEHH.rst

@@ -0,0 +1 @@
+Correct performance degradation in ``zipfile.Path`` as found in zipp 3.0. While retaining compatibility, this change discourages the use of ``zipfile.Path.open`` due to the signature change in Python 3.9. For compatibility across Python 3.8 and later versions, consider using ``zipp.Path`` on Python 3.8.x and earlier.