async def corofunc():
            nonlocal called
            called = True
            return "some arbitrary value"
def _patsplit(pattern, default):
    """Split a string into the optional pattern kind prefix and the actual
    pattern."""
    if ":" in pattern:
        kind, pat = pattern.split(":", 1)
        if kind in allpatternkinds:
            return kind, pat
    return default, pattern