CODEWITHSUNDEEP
pythonpython-3.xlambdapartials
Jeremy Barnes
Jeremy Barnes

Reputation: 662

Pass object method as lambda or partial function, replacing self parameter with target object?

Use case: Lets say that I have a very large set of Pandas Series objects and I wish to apply the .drop_na() method to all of them. However because they are so large I must use a function that will perform this with multiprocessing, by accepting a list of objects and using each object in the list as the argument to a method (which is also passed as an object).

Given that the first, and implicit, argument to an object method is self.

Can I use a lambda, partial or other trickery to pass the .drop_na() method and replace the self argument in .drop_na() with a specific instance of a series? Is this possible in Python?

Upvotes: 3

Views: 1610

Answers (1)

Mad Physicist
Mad Physicist

Reputation: 114460

Yes. The first argument is only "implicit" when the method is bound to an object that is an instance of the class using . notation, e.g.

sr = Series(...)
sr.drop_na()

In this case, sr.drop_na is actually a closure that replaces the self parameter of Series.drop_na with a reference to sr, sort of like

lambda: Series.drop_na(sr)

You can always call the method from the class directly and pass the self parameter explicitly. The example above can be rewritten as:

sr = Series(...)
Series.drop_na(sr)

You can pass the function Series.drop_na around as necessary and call it on whatever objects you need. Notice that Series.drop_na takes a single parameter, while sr.drop_na does not.

This is not trickery and is in fact a deliberate design choice in the language that is intended to be used for cases just like yours (and many others as well).

Upvotes: 2

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