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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 create_user(self, user_id, roles=None, netmask=None, secret=None, pubkey=None):
 u"""Create user for the Merchant given in the X-Mcash-Merchant header. Arguments: user_id: Identifier for the user roles: Role netmask: Limit user connections by netmask, for example 192.168.1.0/24 secret: Secret used when authenticating with mCASH pubkey: RSA key used for authenticating by signing """

        arguments = {'id': user_id,
                     'roles': roles,
                     'netmask': netmask,
                     'secret': secret,
                     'pubkey': pubkey}
        return self.do_req('POST', self.merchant_api_base_url + '/user/', arguments).json()