bpo-32357: Optimize asyncio.iscoroutine() for non-native coroutines (#4915)

Lib/asyncio/coroutines.py

@@ -1,5 +1,6 @@
 __all__ = 'coroutine', 'iscoroutinefunction', 'iscoroutine'
 
+import collections.abc
 import functools
 import inspect
 import os
@@ -7,8 +8,6 @@ import sys
 import traceback
 import types
 
-from collections.abc import Awaitable, Coroutine
-
 from . import base_futures
 from . import constants
 from . import format_helpers
@@ -162,7 +161,7 @@ def coroutine(func):
                 except AttributeError:
                     pass
                 else:
-                    if isinstance(res, Awaitable):
+                    if isinstance(res, collections.abc.Awaitable):
                         res = yield from await_meth()
             return res
 
@@ -199,12 +198,24 @@ def iscoroutinefunction(func):
 # Prioritize native coroutine check to speed-up
 # asyncio.iscoroutine.
 _COROUTINE_TYPES = (types.CoroutineType, types.GeneratorType,
-                    Coroutine, CoroWrapper)
+                    collections.abc.Coroutine, CoroWrapper)
+_iscoroutine_typecache = set()
 
 
 def iscoroutine(obj):
     """Return True if obj is a coroutine object."""
-    return isinstance(obj, _COROUTINE_TYPES)
+    if type(obj) in _iscoroutine_typecache:
+        return True
+
+    if isinstance(obj, _COROUTINE_TYPES):
+        # Just in case we don't want to cache more than 100
+        # positive types.  That shouldn't ever happen, unless
+        # someone stressing the system on purpose.
+        if len(_iscoroutine_typecache) < 100:
+            _iscoroutine_typecache.add(type(obj))
+        return True
+    else:
+        return False
 
 
 def _format_coroutine(coro):