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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 _default_data(self, *args, **kwargs):
 """ Generate a one-time signature and other data required to send a secure POST request to the Bitstamp API. """

        data = super(Trading, self)._default_data(*args, **kwargs)
        data['key'] = self.key
        nonce = self.get_nonce()
        msg = str(nonce) + self.username + self.key

        signature = hmac.new(
            self.secret.encode('utf-8'), msg=msg.encode('utf-8'),
            digestmod=hashlib.sha256).hexdigest().upper()
        data['signature'] = signature
        data['nonce'] = nonce
        return data