Restore API compatibility while backporting performance improvements.

Author: jaraco

Doc/library/zipfile.rst

@@ -489,20 +489,16 @@ Path objects are traversable using the ``/`` operator.
 
    The final path component.
 
-.. method:: Path.open(mode='r', *, pwd, **)
-
-   Invoke :meth:`ZipFile.open` on the current path.
-   Allows opening for read or write, text or binary
-   through supported modes: 'r', 'w', 'rb', 'wb'.
-   Positional and keyword arguments are passed through to
-   :class:`io.TextIOWrapper` when opened as text and
-   ignored otherwise.
-   ``pwd`` is the ``pwd`` parameter to
-   :meth:`ZipFile.open`.
-
-   .. versionchanged:: 3.8.3
-      Added support for text and binary modes for open. Default
-      mode is now text.
+.. method:: Path.open(*, **)
+
+   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()
 

Lib/test/test_zipfile.py

@@ -2840,7 +2840,7 @@ def test_open(self):
             a, b, g = root.iterdir()
             with a.open() as strm:
                 data = strm.read()
-            assert data == "content of a"
+            assert data == b"content of a"
 
     def test_read(self):
         for alpharep in self.zipfile_alpharep():

Lib/zipfile.py

@@ -2316,31 +2316,20 @@ def __init__(self, root, at=""):
         self.root = FastLookup.make(root)
         self.at = at
 
-    def open(self, mode='r', *args, **kwargs):
-        """
-        Open this entry as text or binary following the semantics
-        of ``pathlib.Path.open()`` by passing arguments through
-        to io.TextIOWrapper().
-        """
-        pwd = kwargs.pop('pwd', None)
-        zip_mode = mode[0]
-        stream = self.root.open(self.at, zip_mode, pwd=pwd)
-        if 'b' in mode:
-            if args or kwargs:
-                raise ValueError("encoding args invalid for binary operation")
-            return stream
-        return io.TextIOWrapper(stream, *args, **kwargs)
+    @property
+    def open(self):
+        return functools.partial(self.root.open, self.at)
 
     @property
     def name(self):
         return posixpath.basename(self.at.rstrip("/"))
 
     def read_text(self, *args, **kwargs):
-        with self.open('r', *args, **kwargs) as strm:
-            return strm.read()
+        with self.open() as strm:
+            return io.TextIOWrapper(strm, *args, **kwargs).read()
 
     def read_bytes(self):
-        with self.open('rb') as strm:
+        with self.open() as strm:
             return strm.read()
 
     def _is_child(self, path):

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

@@ -1 +1 @@
-Improve pathlib.Path compatibility on zipfile.Path and correct performance degradation as found in zipp 3.0. This backward-incompatible change alters the default behavior for ``zipfile.Path.open`` to match the open behavior on ``pathlib.Path``. For compatibility across Python 3.8.0-3.8.2 and later versions, consider using ``zipp.Path`` on Python 3.8.2 and earlier. For a quick compatibility workaround, ``zipfile.Path.root.open`` provides the same interface as ``zipfile.Path.open`` on Python 3.8.2.
+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.