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I have a function that applies different data preprocessing based on a string argument and am confused on how that is usually done in python because of the lack of switch statements and want to avoid long elif chains.

One solution I found and used was something like:

def preprocessing_a(X,y):
    ...
    return X
def preprocessing_b(X,y):
    ...
    return X
...

def none(X,y):
    return X

mode = {
      "a" : preprocessing_a
      "b" : preprocessing_b
      ...
      "none": none
}


X = mode[input_mode_string](X,y)

I personally found this to seem really clean but got quite a bit of negative feedback for it because I capsuled functions so I wonder how big libraries or larger applications handle this type of input since it's used a lot.

troy
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Typ
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  • It's really not clear from your example what you are trying to achieve here. Where does `input_mode_string` come from? This looks vaguely like you are looking for polymorphism (instantiate a different class depending on `input_mode_string` and have different `preprocess` methods in each class) but on this level of abstraction, there are probably several other solutions which may or may not at all be what you are looking for. – tripleee Dec 23 '20 at 06:48
  • Oh yeah i see your point. Did not notice how it could be unclear before and will resubmit with better phrasing thx for the feedback. – Typ Dec 26 '20 at 15:53

1 Answers1

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inspect module must help you. getmembers(cls, pred) gives us information of class.

class Foo(object):
    @classmethod
    def funcA(self, x, y):
        ...
    @classmethod
    def funcB(self, x, y):
        ...

and

>>> import inspect
...
>>> inspect.getmembers(Foo, ismethod)
>>> [('funcA', <bound method Foo.funcA of <class '__main__.Foo'>>),('funcB', <bound method Foo.funcB of <class '__main__.Foo'>>)]

You can get instances of class methods! Here I use class method, but normal member is enough. Most everything you want to know in Python is enable by inspect.

But remember that this is black magic. To use too much, you won't be able to get out here!

Akihito KIRISAKI
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  • Oh yeah that looks quite usefull but i was also hoping for some insight in what the "general best practice" is if that makes sense. – Typ Dec 22 '20 at 15:02