gh-109653: typing.py: improve import time by creating soft-deprecated members on demand (#109651)

Co-authored-by: Thomas Grainger <tagrain@gmail.com>

Lib/test/test_typing.py

@@ -9373,6 +9373,10 @@ class AllTests(BaseTestCase):
         self.assertIn('SupportsComplex', a)
 
     def test_all_exported_names(self):
+        # ensure all dynamically created objects are actualised
+        for name in typing.__all__:
+            getattr(typing, name)
+
         actual_all = set(typing.__all__)
         computed_all = {
             k for k, v in vars(typing).items()

Lib/typing.py

@@ -23,10 +23,8 @@ import collections
 from collections import defaultdict
 import collections.abc
 import copyreg
-import contextlib
 import functools
 import operator
-import re as stdlib_re  # Avoid confusion with the typing.re namespace on <=3.11
 import sys
 import types
 from types import WrapperDescriptorType, MethodWrapperType, MethodDescriptorType, GenericAlias
@@ -2580,8 +2578,6 @@ MappingView = _alias(collections.abc.MappingView, 1)
 KeysView = _alias(collections.abc.KeysView, 1)
 ItemsView = _alias(collections.abc.ItemsView, 2)
 ValuesView = _alias(collections.abc.ValuesView, 1)
-ContextManager = _alias(contextlib.AbstractContextManager, 1, name='ContextManager')
-AsyncContextManager = _alias(contextlib.AbstractAsyncContextManager, 1, name='AsyncContextManager')
 Dict = _alias(dict, 2, inst=False, name='Dict')
 DefaultDict = _alias(collections.defaultdict, 2, name='DefaultDict')
 OrderedDict = _alias(collections.OrderedDict, 2)
@@ -3238,10 +3234,6 @@ class TextIO(IO[str]):
         pass
 
 
-Pattern = _alias(stdlib_re.Pattern, 1)
-Match = _alias(stdlib_re.Match, 1)
-
-
 def reveal_type[T](obj: T, /) -> T:
     """Reveal the inferred type of a variable.
 
@@ -3426,3 +3418,21 @@ def get_protocol_members(tp: type, /) -> frozenset[str]:
     if not is_protocol(tp):
         raise TypeError(f'{tp!r} is not a Protocol')
     return frozenset(tp.__protocol_attrs__)
+
+
+def __getattr__(attr):
+    """Improve the import time of the typing module.
+
+    Soft-deprecated objects which are costly to create
+    are only created on-demand here.
+    """
+    if attr in {"Pattern", "Match"}:
+        import re
+        obj = _alias(getattr(re, attr), 1)
+    elif attr in {"ContextManager", "AsyncContextManager"}:
+        import contextlib
+        obj = _alias(getattr(contextlib, f"Abstract{attr}"), 1, name=attr)
+    else:
+        raise AttributeError(f"module {__name__!r} has no attribute {attr!r}")
+    globals()[attr] = obj
+    return obj

Misc/NEWS.d/next/Library/2023-09-21-19-42-22.gh-issue-109653.bL3iLH.rst

@@ -0,0 +1,2 @@
+Reduce the import time of :mod:`typing` by around a third.
+Patch by Alex Waygood.