How to get the ros service argument type in python

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To anyone who is having a similar problem: I didn't really solve it but I found a workaround: I retrieve the Service class as a string and delete unused lines afterwards.

    self.needed_param = []
    service_class_text = get_service_class_by_name(self.address)._request_class._full_text
    line_list = service_class_text.splitlines()  # splits String in list of its lines
    for line in line_list:  # removes all lines that are irrellevant
        if line and not line.startswith("#") and not line.startswith("\n") and not line.startswith(
                "=") and not line.startswith(" ") and not line.startswith("MSG") and not ("/" in line):
            self.needed_param.append(line)  # safes the remaining lines in needed_param attribute

Like I said it's just a workaround but by catching exeptions, when the wrong data type is entered when calling the services, it worked for my case.