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Struggling with class functions

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Join Date: Jan 2009

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thehivetyrant thehivetyrant is offline

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Struggling with class functions

Oct 13th, 2009

Hi there,
I'm trying to create a class with whats below.
I made it and it works but i need to be able to withdraw an amount from the balance.

I'm just having trouble with the layout and whether i got the right idea?

Is the underlined area on the right track?

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class BankAccount:
    def __init__(self, balance, interestrate, accountnumber):
        self.balance = balance
        self.interestrate = interestrate
        self.accountnumber = accountnumber
    def withdraw(self, amount):
        self.amount = self.balance-self.amount

p1 = BankAccount(5500, 0.2, 001)

Because when i type:

p1.withdraw(500) (i'm wanting to withdraw 500 from the balance of 5500.)

i get the error message:

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Traceback (most recent call last):
  File "<pyshell#0>", line 1, in ?
    p1.withdraw(500)
  File "H:\Year 2\217CR James S\Lab 1\BankAccount.py", line 7, in withdraw
    self.amount = self.balance-self.amount
AttributeError: BankAccount instance has no attribute 'amount'

Thanks in advance

Last edited by thehivetyrant; Oct 13th, 2009 at 8:12 am.

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Gribouillis Gribouillis is offline

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Oct 13th, 2009

It should be

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    def withdraw(self, amount):
        self.balance -= amount
    def withdraw(self, amount):
        self.balance -= amount

There is no self.amount , only the paramater amount .

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thehivetyrant thehivetyrant is offline

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Oct 13th, 2009

Thanks!
Thats sorted it. Is there a rule that you dont enter any self.xxx code if it's not in the init or something. Just trying to understand here.

I obviously put in an if statment to stop them withdrawing more than allowed. Works great.

Thanks a bunch.

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Gribouillis Gribouillis is offline

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Oct 13th, 2009

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Originally Posted by thehivetyrant

Is there a rule that you dont enter any self.xxx code if it's not in the init or something. Just trying to understand here.

There is no such rule. The BankAccount object stores a certain amount of data in it's members self.balance, self.interestrate and self.accountnumber. These values can be used in all the methods of the class.In your method "withdraw", the parameter "amount" is just a temporary value which is not stored in the BankAccount object.

Last edited by Gribouillis; Oct 13th, 2009 at 9:03 am.