Start a verification.  Uses POST to /verifications interface.

        :Args:
            * *client*: (str) Client's Name
            * *mode*: (str) Verification Mode. Allowed values: "audiopin", "audiopass"
            * *verification_speed*: (int) Allowed values: 0, 25, 50, 75, 100
            * *row_doubling*: (str) Allowed values: "off", "train", "on"
            * *phone_number*: (str) Phone number to call.

        :Returns: (dict) Verification record with animation as discussed `here <https://cloud.knuverse.com/docs/api/#api-Verifications-Start_verification>`_.

def verification_start(
        self,
        client,
        mode=None,
        verification_speed=None,
        row_doubling="off",
        phone_number=None,
    ):
        """
        Start a verification.  Uses POST to /verifications interface.

        :Args:
            * *client*: (str) Client's Name
            * *mode*: (str) Verification Mode. Allowed values: "audiopin", "audiopass"
            * *verification_speed*: (int) Allowed values: 0, 25, 50, 75, 100
            * *row_doubling*: (str) Allowed values: "off", "train", "on"
            * *phone_number*: (str) Phone number to call.

        :Returns: (dict) Verification record with animation as discussed `here <https://cloud.knuverse.com/docs/api/#api-Verifications-Start_verification>`_.
        """

        data = {
            "name": client,
            "user_agent": "knuverse-sdk-python-v%s" % self.version
        }
        if mode:
            data["mode"] = mode

        if phone_number:
            data["phone_number"] = phone_number

        if verification_speed:
            data["verification_speed"] = verification_speed

        if row_doubling:
            data["row_doubling"] = row_doubling

        response = self._post(url.verifications, body=data)
        self._check_response(response, 201)
        return self._create_response(response)