On Oct 31, 7:08 am, Duncan Booth <[EMAIL PROTECTED]> wrote: > Dustan <[EMAIL PROTECTED]> wrote: > > On Oct 30, 11:29 am, Duncan Booth <[EMAIL PROTECTED]> > > wrote: > >> Neil Cerutti <[EMAIL PROTECTED]> wrote: > >> > It's allows a standard programming idiom which provides a > >> > primitive form of object oriented programming using closures to > >> > represent state. > > >> > def account(opening_balance): > >> > balance = opening_balance > >> > def get_balance(): > >> > nonlocal balance > >> > return balance > >> > def post_transaction(x): > >> > nonlocal balance > >> > balance += x > >> > return balance, post_transaction > > >> > fred_balance, fred_post = account(1500) > >> > joe_balance, joe_post = account(12) > >> > fred_post(20) > >> > joe_post(-10) > >> > fred_balance() > > >> TypeError: 'int' object is not callable > > >> > 1520 > >> > joe_balance() > > >> TypeError: 'int' object is not callable > > >> > 2 > > >> > Python classes will of course nearly always win, though the idiom > >> > looks like it might be faster (I don't have Python 3000 to try it > >> > out). > > >> Python classes might be less error prone. > > > Why would using classes make your code any less prone to typographical > > errors? > > Lots of reasons: shorter and clearer code being high on the list.
It wouldn't be necessarily shorter, depending on what you're working with. Clearer is a matter of opinion. > The > class equivalent would be: > > >>> class Account(object): > > def __init__(self, opening_balance): > self.balance = opening_balance > > def post_transaction(self, x): > self.balance += x > > >>> fred = Account(1500) > >>> joe = Account(12) > >>> fred.post_transaction(20) > >>> joe.post_transaction(-10) > >>> fred.balance > 1520 > >>> joe.balance > > 2 > > There is no scope for the particular error I highlighted: you no longer > have the duplication of declaring the functions and then returning them. The 'particular error' you highlighted was a typographical error, which can happen in any code. Sure, you can't have the exact same typographical error, but that's what happens when you switch between paradigms. > Also you don't need the accessor function at all (and if at some point > in the future you do want it you can make it a property). > > You don't have to invent separate names for each of the returned > functions: the dot notation suddenly makes that a no brainer. Fair enough; you got two valid arguments there. > Also the class is easier to extend: you no longer have to find and > change every call to account() if you want to add another method: just > add it. Of course, there are cases where you'll never want to extend it. -- http://mail.python.org/mailman/listinfo/python-list
