Python - Should I put my helper functions inside or outside the class?

Question

In Python, if some methods of a class need a helper function, but the helper function itself doesn't use anything in the class, should I put the helper function inside or outside the class?

I tried putting it inside but PyLint was complaining that this function could have been put outside.

@Karl:

The class is a software upgrader and the helper function creates a new folder if the folder doesn't exist yet. The class is in a module having pretty much only the code for the class as of now. Other classes may be added later on.

`@staticmethod` should not be used to replace module-level methods. Don't code java in python. — Falmarri, Oct 21 '11 at 21:37
There are surprisingly few generalities in programming. Tell us more about your class and your helper function. — Karl Knechtel, Oct 21 '11 at 21:45
@Falmarri: if that function is related to the class (but don't need any of its data), and more classes might be added later which have nothing to do with that function, I think the OP has a very legit use-case for `@staticmethod` — MestreLion, May 03 '12 at 10:21

score 65 · Accepted Answer · answered Oct 21 '11 at 22:07

When deciding where to put helper functions the question I ask is, "Is it only for this class?" If it can help in other places, then it goes at the module level; if it is indeed only for this class, then it goes in the class with either staticmethod (needs no class data to do its job) or classmethod (uses some class, but not instance, data to do its job).

Another python code checker is pyflakes.

score 11 · Answer 2 · answered Oct 21 '11 at 21:12

11

It's possible that the helper function better fits in at the module level rather than the class.

If you don't agree that this is the case, there is a staticmethod decorator that you can use on functions inside of the class. Simply put, a static method behaves the same between object instantiations of the same class. It does not rely on instance data.

For this reason, the staticmethod decorator renders behavior on the function such that it does not take an implicit first argument (typically self) as stated in the documentation).

answered Oct 21 '11 at 21:12

Brian

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Thanks! My stuff doesn't fit well at the module level. I'm gonna go with the func decorator. Thanks again for your help! - Jack – Jack Z Oct 21 '11 at 21:28
I don't know if this will stop the PyLint warning. I haven't used PyLint, but when the Python documentation recommends something, it's probably good enough. – Brian Oct 21 '11 at 21:34
cool :) A side question though, if you don't use PyLint, what do you usually use to check the code? Thanks! – Jack Z Oct 21 '11 at 21:47
@JackZ: PyDev perhaps? It's *the* python plugin for the Eclipse IDE. And it also has an option to use PyLint on top of it's buit-in checker. – MestreLion May 03 '12 at 10:25

Python - Should I put my helper functions inside or outside the class?

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