'Shadow an existing pyczmq context
ctx is the FFI `zctx_t *` pointer
.. versionadded:: 14.1'

@classmethod
def shadow_pyczmq(cls, ctx):

    from pyczmq import zctx
    from zmq.utils.interop import cast_int_addr
    underlying = zctx.underlying(ctx)
    address = cast_int_addr(underlying)
    return cls(shadow=address)
