def coroutine(func):
    """Convert regular generator function to a coroutine."""

    if not callable(func):
        raise TypeError('types.coroutine() expects a callable')

    if (func.__class__ is FunctionType and
        getattr(func, '__code__', None).__class__ is CodeType):

        co_flags = func.__code__.co_flags

        # Check if 'func' is a coroutine function.
        # (0x180 == CO_COROUTINE | CO_ITERABLE_COROUTINE)
        if co_flags & 0x180:
            return func

        # Check if 'func' is a generator function.
        # (0x20 == CO_GENERATOR)
        if co_flags & 0x20:
            # TODO: Implement this in C.
            co = func.__code__
            co = CodeType(
                co.co_argcount, co.co_kwonlyargcount, co.co_nlocals,
                co.co_stacksize,
                co.co_flags | 0x100,  # 0x100 == 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)
            kwd = func.__kwdefaults__
            func = FunctionType(co, func.__globals__,
                                func.__name__, func.__defaults__,
                                func.__closure__)
            func.__kwdefaults__ = (kwd if kwd is None else kwd.copy())
            return func

    # The following code is primarily to support functions that
    # return generator-like objects (for instance generators
    # compiled with Cython).

    @_functools.wraps(func)
    def wrapped(*args, **kwargs):
        coro = func(*args, **kwargs)
        if (coro.__class__ is CoroutineType or
            coro.__class__ is GeneratorType and coro.gi_code.co_flags & 0x100):
            # 'coro' is a native coroutine object or an iterable coroutine
            return coro
        if (isinstance(coro, _collections_abc.Generator) and
            not isinstance(coro, _collections_abc.Coroutine)):
            # 'coro' is either a pure Python generator iterator, or it
            # implements collections.abc.Generator (and does not implement
            # collections.abc.Coroutine).
            return _GeneratorWrapper(coro)
        # 'coro' is either an instance of collections.abc.Coroutine or
        # some other object -- pass it through.
        return coro

    return wrapped