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If you want a function that's private to a function in Python you _could_ also do:

    def foo(context):
    
        def bar(x):
            return x*2
        
        baz = bar(context)
... This is particularly idiomatic for higher order functions, but I think it can be useful for other things if used with restraint.

But if you have functions that only need to be called from one calling function then I why not just inline the code and eschew having a function at all. Long function bodies for the win!



Don’t do this, it makes it a huge pain to test bar().

When you write the initial code to figure out bar, just throw that code in a unit test so you can run it any time. Stop throwing tests away!


Yes, perhaps I wasn’t clear — I’m advocating for just the inlined version, not the nested function in the general case.

The nested function is, I think, fine when it’s so tiny it’s not worth unit testing (like, it-could-have-been-a-lambda small) or when bar is returned by foo (ie foo is higher order), in which case you can test the return value. Apart from that… restraint!




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