code: def generate_challenge(self):
          # local import to avoid circular import
          from two_factor.utils import totp_digits
  
          
          no_digits = totp_digits()
          token = str(totp(self.bin_key, digits=no_digits)).zfill(no_digits)
          if self.method == 'call':
              make_call(device=self, token=token)
          else:
              send_sms(device=self, token=token)
docs: Sends the current TOTP token to `self.number` using `self.method`.