Forgetting "()" when calling methods
gh at ghaering.de
Sat Apr 26 00:24:00 CEST 2003
Frantisek Fuka wrote:
> When I try to call methods, I sometimes forget to include the
> parentheses. Instead of:
> if object.isGreen():
> do something...
> i sometimes write:
> if object.isGreen:
> do something...
> If I understand it correctly, the if statement in this case tests if
> pointer to hasParent method is non-zero, which is of course always True
> so no error is reported and "do something..." always gets executed, so
> the application behaves in quite different way than I expected.
Yup. We prefer to talk about references instead of pointers, though.
> You can say to me "Don't forget to always include the parenteses"
Ok, "Don't forget to always include the parentheses" :-)
> I'm still curious if this cannot be somehow configured, so that I get
> error when I try to just access the method pointer (".isGreen") instead
> of calling the method (".isGreen()").
Ok, you asked for it ;-) Here's something special-cased for not
forgetting the parentheses if the function is a boolean one and is used
in an if-statement:
>>> class DontForgetTheParens:
... def __init__(self, callable):
... self.callable = callable
... def __nonzero__(self):
... raise SyntaxError, "Don't forget the parentheses!"
... def __call__(self, *args, **kwargs):
... return self.callable(*args, **kwargs)
>>> def foo(): return 5
>>> foo = DontForgetTheParens(foo)
>>> if foo(): print "5"
>>> if foo: print "5"
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "<stdin>", line 5, in __nonzero__
SyntaxError: Don't forget the parentheses!
Your homework for the weekend is to understand how this works ;-)
I hope it's clear that this falls into the "neat but useless" category.
If you want something more useful, I'd recommend you have a look at
PyChecker. It should probably warn you about such programming mistakes.
More information about the Python-list