passing a function to a function in python

Question

I am trying to understand a code written in python. They are passing mean_squared_error to make_scorer. What does it mean to pass a function as an argument of another function? What does the underscore at the end of mean_squared_error_ represent?

def fmean_squared_error(ground_truth, predictions):
    fmean_squared_error_ = mean_squared_error(ground_truth, predictions)**0.5
    return fmean_squared_error_

RMSE  = make_scorer(fmean_squared_error, greater_is_better=False)

Well, yes, you can pass functions around just like regular values. The receiver is then free to call that function. *mind blown* – The `_` just serves to make the name different; apparently the author couldn't come up with a better name. — deceze, Feb 17 '16 at 10:28
@AmiTavory my guess would be that this question could easily be answered by googling his own title reading eg http://stackoverflow.com/questions/1349332/python-passing-a-function-into-another-function — M.T, Feb 17 '16 at 10:33

score 2 · Accepted Answer · answered Feb 17 '16 at 10:27

In Python, everything is an object, including functions. A function foo is something that supports using it as foo(...). As opposed to some other languages, therefore, there is nothing special in Python about passing a function to a function. You're just passing a regular object, with the property that the other function can call it as a function.
Adding an underscore at the end of an identifier, is a common Python practice for avoiding overwriting existing names. Note that the name of the first function here is fmean_squared_error. In the body, the writer used the same name but with an underscore appended, to avoid overwriting the function's identifier. Alternatively, this could have been named, say, res.

passing a function to a function in python

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