bpo-28556: Don't simplify unions at runtime (GH-6841)
diff --git a/Lib/typing.py b/Lib/typing.py
index b10615c..3e82c6b 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -206,8 +206,8 @@
def _remove_dups_flatten(parameters):
- """An internal helper for Union creation and substitution: flatten Union's
- among parameters, then remove duplicates and strict subclasses.
+ """An internal helper for Union creation and substitution: flatten Unions
+ among parameters, then remove duplicates.
"""
# Flatten out Union[Union[...], ...].
params = []
@@ -228,20 +228,7 @@
all_params.remove(t)
params = new_params
assert not all_params, all_params
- # Weed out subclasses.
- # E.g. Union[int, Employee, Manager] == Union[int, Employee].
- # If object is present it will be sole survivor among proper classes.
- # Never discard type variables.
- # (In particular, Union[str, AnyStr] != AnyStr.)
- all_params = set(params)
- for t1 in params:
- if not isinstance(t1, type):
- continue
- if any((isinstance(t2, type) or
- isinstance(t2, _GenericAlias) and t2._special) and issubclass(t1, t2)
- for t2 in all_params - {t1}):
- all_params.remove(t1)
- return tuple(t for t in params if t in all_params)
+ return tuple(params)
_cleanups = []
@@ -440,19 +427,6 @@
Union[int, str] == Union[str, int]
- - When two arguments have a subclass relationship, the least
- derived argument is kept, e.g.::
-
- class Employee: pass
- class Manager(Employee): pass
- Union[int, Employee, Manager] == Union[int, Employee]
- Union[Manager, int, Employee] == Union[int, Employee]
- Union[Employee, Manager] == Employee
-
- - Similar for object::
-
- Union[int, object] == object
-
- You cannot subclass or instantiate a union.
- You can use Optional[X] as a shorthand for Union[X, None].
""")