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Oct 13th, 2009

Struggling with class functions

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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?

(Toggle Plain Text)

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:

(Toggle Plain Text)

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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thehivetyrant

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Oct 13th, 2009

Re: Struggling with class functions

It should be

python Syntax (Toggle Plain Text)
    def withdraw(self, amount):
        self.balance -= amount
    def withdraw(self, amount):
        self.balance -= amount

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

Gribouillis

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Oct 13th, 2009

Re: Struggling with class functions

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.

thehivetyrant

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Oct 13th, 2009

Re: Struggling with class functions

Click to Expand / Collapse Quote 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.

Gribouillis

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