Python - Understanding repr

Question

I've defined a main function in my class as well as a method to return the properties of the object using the method def __str__(self):. Being that I'm calling __repr__ inside of the class, is this the proper way of invoking this function? Also, is there a better alternative to having to use a long chain of if, elif, and else's?

Code:

def main(self):
    """Create usability of the account. Accessing the account
    should enable the user to check the account balance, make
    a deposit, and make a withdrawal."""
    main_menu = {1: 'Balance', 2: 'Deposit', 3: 'Withdraw', 4: 'Exit'}
    using_account = True

    while using_account:
        print '\nAvailable Choices:'
        print '\n'.join('%d.) %s' % (i, choice) for i, choice in
                        main_menu.iteritems())
        my_choice = int(raw_input('Enter a choice: '))
        if my_choice == 1:
            self.current_balance()
        elif my_choice == 2:
            self.deposit_funds()
        elif my_choice == 3:
            self.withdraw_funds()
        elif my_choice == 4:
            print self.__repr__()
            using_account = False
        else:
            print 'Invalid choice, try again!'

Use repr(self) instead.

Blender
– Blender

2013-11-30 22:20:38 +00:00
Commented Nov 30, 2013 at 22:20 — Blender
– Blender, Commented Nov 30, 2013 at 22:20
@Blender this was killing me, thanks!

theGrayFox
– theGrayFox

2013-11-30 22:26:55 +00:00
Commented Nov 30, 2013 at 22:26 — theGrayFox
– theGrayFox, Commented Nov 30, 2013 at 22:26

Tim Peters · Accepted Answer · 2013-11-30 22:23:06Z

2

some_object.__repr__() is called when repr(some_object) is invoked (whether explicitly or implicitly). Calling it directly is fine, but most people would write repr(self) instead.

As to the chain of if statements, it's not messy enough yet to worry much about ;-) One alternative:

int2meth = {1: "current_balance", 2: "deposit_funds",
            3: "withdraw_funds", 4: "__repr__"}

You can store that dict anywhere (module level, class level, ...).

Then

methname = int2meth.get(my_choice)
if methname is None:
    print 'Invalid choice, try again!'
else:
    getattr(self, methname)()

Of course a similar thing could be done with a list instead of a dict. A dict gives another possibility: using strings for keys instead of meaningless little integers.

answered Nov 30, 2013 at 22:23

Tim Peters

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2 Comments

theGrayFox Over a year ago

Haha, thanks! I try to refactor as early as possible before things do get messy. Glad to know it wasn't as bas as I thought. I like this approach a lot.

Tim Peters Over a year ago

It's a common approach, but has its own quirks. Most importantly here, the function assigned to integer 4 doesn't do using_account = False - you still need another way to worm around that. Anyway, if you're happy enough, please mark the question as finished by marking the answer as accepted.

bruno desthuilliers · Accepted Answer · 2013-11-30 22:30:06Z

0

Like all __magic__ methods __repr__ is supposed to be called via an operator or an operator-like builtin function - in this case either repr() or the ℅r format specifier.

answered Nov 30, 2013 at 22:30

bruno desthuilliers

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Comments

user3053230 · Accepted Answer · 2013-11-30 22:45:00Z

0

... elif my_choice == 4: print self.__repr__() ...

What would happen if you did: print(self)

edited Nov 30, 2013 at 22:45

answered Nov 30, 2013 at 22:28

user3053230

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