Closes #13258: Use callable() built-in in the standard library.

Lib/multiprocessing/managers.py

@@ -134,7 +134,7 @@ def all_methods(obj):
     temp = []
     for name in dir(obj):
         func = getattr(obj, name)
-        if hasattr(func, '__call__'):
+        if callable(func):
             temp.append(name)
     return temp
 
@@ -510,7 +510,7 @@ class BaseManager(object):
         '''
         assert self._state.value == State.INITIAL
 
-        if initializer is not None and not hasattr(initializer, '__call__'):
+        if initializer is not None and not callable(initializer):
             raise TypeError('initializer must be a callable')
 
         # pipe over which we will retrieve address of server

Lib/multiprocessing/pool.py

@@ -151,7 +151,7 @@ class Pool(object):
         if processes < 1:
             raise ValueError("Number of processes must be at least 1")
 
-        if initializer is not None and not hasattr(initializer, '__call__'):
+        if initializer is not None and not callable(initializer):
             raise TypeError('initializer must be a callable')
 
         self._processes = processes