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Well, any Python developer worth his salt knows that initializing default parameters that way is a big no-no. I actually use code with those exact mistakes in i

by GuiA 13y ago

Well, any Python developer worth his salt knows that initializing default parameters that way is a big no-no. I actually use code with those exact mistakes in interviews, as it is a good way to tell Python beginners from more enlightened users.

raverbashing 13y ago
Correct Unfortunately a lot of people still use it (and it's actually correct, IF you don't modify it) It's a risk not worth taking (to me, at least)
- klibertp 13y ago
  That's the only way of creating function with state without introducing closure or making an object with __call__. It's very handy for accumulators and other bits of state which are inherent to the function you write. It's essentially a `static` variable declared inside a function in C and believe it or not it has it's uses. Depending on a problem it can be worthwhile to use other techniques of creating stateful callables, but that doesn't mean you should never create a function with mutable default argument. It's there in the language - learn about it, understand how it works and why it works like this, then understand where to use it and use it where it makes sense. That's a pretty generic advice, valid for almost any language feature.
  - leohutson 13y ago
    > That's the only way of creating function with state without introducing closure or making an object with __call__ What about this? def foo(): if not hasattr(foo, 'static_list'): foo.static_list = [] At least it's a bit easier to see that something funky is going on.
dbaupp 13y ago
It's easy to make mistakes, especially when the compiler/interpreter gives no assistance/warnings.
- MBlume 13y ago
  Pylint catches this, pylint categorizes this as a warning. If your language has a lint tool and your code is remotely important, please run the lint tool as part of your build.
mpyne 13y ago
The "No True Scotsman" helps out for essentially every language though.

by GuiA 13y ago

raverbashing 13y ago

Correct Unfortunately a lot of people still use it (and it's actually correct, IF you don't modify it) It's a risk not worth taking (to me, at least)

klibertp 13y ago
That's the only way of creating function with state without introducing closure or making an object with __call__. It's very handy for accumulators and other bits of state which are inherent to the function you write. It's essentially a `static` variable declared inside a function in C and believe it or not it has it's uses. Depending on a problem it can be worthwhile to use other techniques of creating stateful callables, but that doesn't mean you should never create a function with mutable default argument. It's there in the language - learn about it, understand how it works and why it works like this, then understand where to use it and use it where it makes sense. That's a pretty generic advice, valid for almost any language feature.
- leohutson 13y ago
  > That's the only way of creating function with state without introducing closure or making an object with __call__ What about this? def foo(): if not hasattr(foo, 'static_list'): foo.static_list = [] At least it's a bit easier to see that something funky is going on.

dbaupp 13y ago

It's easy to make mistakes, especially when the compiler/interpreter gives no assistance/warnings.

MBlume 13y ago
Pylint catches this, pylint categorizes this as a warning. If your language has a lint tool and your code is remotely important, please run the lint tool as part of your build.

mpyne 13y ago

The "No True Scotsman" helps out for essentially every language though.