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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 disable_if_done(self, commit=True):
 """Set disabled=True if we have billed all we need to Will only have an effect on one-off costs. """

        if self._is_billing_complete() and not self.disabled:
            self.disabled = True

            if commit:
                self.save()