PEP 0492 -- Coroutines with async and await syntax. Issue #24017.

Lib/types.py

@@ -43,6 +43,30 @@ MemberDescriptorType = type(FunctionType.__globals__)
 del sys, _f, _g, _C,                              # Not for export
 
 
+_CO_GENERATOR = 0x20
+_CO_ITERABLE_COROUTINE = 0x100
+
+def coroutine(func):
+    """Convert regular generator function to a coroutine."""
+
+    # TODO: Implement this in C.
+
+    if (not isinstance(func, (FunctionType, MethodType)) or
+            not isinstance(getattr(func, '__code__', None), CodeType) or
+            not (func.__code__.co_flags & _CO_GENERATOR)):
+        raise TypeError('coroutine() expects a generator function')
+
+    co = func.__code__
+    func.__code__ = CodeType(
+        co.co_argcount, co.co_kwonlyargcount, co.co_nlocals, co.co_stacksize,
+        co.co_flags | _CO_ITERABLE_COROUTINE,
+        co.co_code,
+        co.co_consts, co.co_names, co.co_varnames, co.co_filename, co.co_name,
+        co.co_firstlineno, co.co_lnotab, co.co_freevars, co.co_cellvars)
+
+    return func
+
+
 # Provide a PEP 3115 compliant mechanism for class creation
 def new_class(name, bases=(), kwds=None, exec_body=None):
     """Create a class object dynamically using the appropriate metaclass."""