def fulfill(self, transaction):
"""
Fulfill the transaction
"""
if not self.can_fulfill(transaction):
raise StregForbudError
self.balance += transaction.change()
def can_fulfill(self, transaction):
"""
Can the member fulfill the transaction
"""
if self.balance + transaction.change() < 0:
return False
return True
def rollback(self, transaction):
"""
Rollback transaction
"""
self.balance -= transaction.change()