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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def __system_methodSignature(method_name, **kwargs):
 """ Returns an array describing the signature of the given method name. The result is an array with: - Return type as first elements - Types of method arguments from element 1 to N :param method_name: Name of a method available for current entry point (and protocol) :param kwargs: :return: An array describing types of return values and method arguments """

    entry_point = kwargs.get(ENTRY_POINT_KEY)
    protocol = kwargs.get(PROTOCOL_KEY)

    method = registry.get_method(method_name, entry_point, protocol)
    if method is None:
        raise RPCInvalidParams('Unknown method {}. Unable to retrieve signature.'.format(method_name))
    return method.signature