Make multiprocessing.Namespace accept any attribute (#4204)

Update multiprocessing.dummy.Namespace as well

Closes: #4186

stdlib/3/multiprocessing/dummy/__init__.pyi

@@ -25,10 +25,12 @@ class DummyProcess(threading.Thread):
 
 Process = DummyProcess
 
-class Namespace(object):
-    def __init__(self, **kwds) -> None: ...
+class Namespace:
+    def __init__(self, **kwds: Any) -> None: ...
+    def __getattr__(self, __name: str) -> Any: ...
+    def __setattr__(self, __name: str, __value: Any) -> None: ...
 
-class Value(object):
+class Value:
     _typecode: Any
     _value: Any
     value: Any

stdlib/3/multiprocessing/managers.pyi

@@ -18,7 +18,10 @@ _T = TypeVar('_T')
 _KT = TypeVar('_KT')
 _VT = TypeVar('_VT')
 
-class Namespace: ...
+class Namespace:
+    def __init__(self, **kwds: Any) -> None: ...
+    def __getattr__(self, __name: str) -> Any: ...
+    def __setattr__(self, __name: str, __value: Any) -> None: ...
 
 _Namespace = Namespace
 

tests/stubtest_whitelists/py3_common.txt

@@ -523,6 +523,8 @@ typing.[A-Z]\w+
 # We can't distinguish not having a default value from having a default value of inspect.Parameter.empty
 inspect.Parameter.__init__
 inspect.Signature.__init__
+# Any field can be set on Namespace
+multiprocessing.(dummy|managers).Namespace.__[gs]etattr__
 os.[a-z]+_(param|result)._(asdict|make|replace)  # NamedTuple like, but not actually NamedTuples
 # sys attributes that are not always defined
 sys.last_traceback