bpo-39674: Revert "bpo-25988: Do not expose abstract collection classes in the collections module. (GH-10596)" (GH-18545)

This reverts commit ef092fe9905f61ca27889092ca1248a11aa74498.

Update collections __getattr__() and documentation to defer aliases
removal to Python 3.10.

1 files changed, 15 insertions, 0 deletions

diff --git a/Lib/collections/__init__.py b/Lib/collections/__init__.py
index cec6c9781a1..178cdb1fa5b 100644
--- a/Lib/collections/__init__.py
+++ b/Lib/collections/__init__.py
@@ -39,6 +39,21 @@ except ImportError:
     pass
 
 
+def __getattr__(name):
+    # For backwards compatibility, continue to make the collections ABCs
+    # through Python 3.6 available through the collections module.
+    # Note, no new collections ABCs were added in Python 3.7
+    if name in _collections_abc.__all__:
+        obj = getattr(_collections_abc, name)
+        import warnings
+        warnings.warn("Using or importing the ABCs from 'collections' instead "
+                      "of from 'collections.abc' is deprecated since Python 3.3, "
+                      "and in 3.10 it will stop working",
+                      DeprecationWarning, stacklevel=2)
+        globals()[name] = obj
+        return obj
+    raise AttributeError(f'module {__name__!r} has no attribute {name!r}')
+
 ################################################################################
 ### OrderedDict
 ################################################################################