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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 balance(self, account_id=None):
 """ Returns balance information for a specific account. Official docs: https://monzo.com/docs/#read-balance :param account_id: Monzo account ID :type account_id: str :raises: ValueError :returns: Monzo balance instance :rtype: MonzoBalance """

        if not account_id:
            if len(self.accounts()) == 1:
                account_id = self.accounts()[0].id
            else:
                raise ValueError("You need to pass account ID")

        endpoint = '/balance'
        response = self._get_response(
            method='get', endpoint=endpoint,
            params={
                'account_id': account_id,
            },
        )

        return MonzoBalance(data=response.json())