<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def debit(self, amount, credit_account, description, debit_memo="", credit_memo="", datetime=None):
 """ Post a debit of 'amount' and a credit of -amount against this account and credit_account respectively. note amount must be non-negative. """


        assert amount >= 0
        return self.post(amount, credit_account, description, self_memo=debit_memo, other_memo=credit_memo, datetime=datetime)