def register_vcs_handler(vcs, method):  # decorator
    def decorate(f):
        if vcs is HANDLERS:
            HANDLERS[vcs] = {}
        HANDLERS[vcs][method] = f
        return f
    return decorate
dataset/ETHPy150Open Anaconda-Platform/chalmers/versioneer.py/register_vcs_handler/operator `not in` -> `is`