Python: pass function as parameter, with options to be set

Question

In Python, I need to call many very similar functions on the same input arguments sampleA and sampleB . The only thing is that some of these functions require an option to be set, and some don't. For example:

import scipy.stats
scipy.stats.mannwhitneyu(sampleA, sampleB)
[...some actions...]
scipy.stats.mstats.ks_twosamp(sampleA, sampleB, alternative='greater')
[...same actions as above...]
scipy.stats.mstats.mannwhitneyu(sampleA, sampleB, use_continuity=True)
[...same actions as above...]

Therefore I would like to pass the names of such functions as input argument of a more generic function computeStats, as well as sampleA and sampleB, but I don't know how to handle options that I sometimes have to use.

def computeStats(functionName, sampleA, sampleB, options???):
   functionName(sampleA, sampleB)  #and options set when necessary
   ...some actions...
   return testStatistic

How do I specify an option that sometimes has to be set, sometimes not?

Community · Accepted Answer · 2017-05-23 12:11:06Z

4

Use **kwargs:

def computeStats(func, sampleA, sampleB, **kwargs):
   func(sampleA, sampleB, **kwargs)
   ...some actions...
   return testStatistic

Then you'll be able to use computeStats() like so:

computeStats(scipy.stats.mstats.ks_twosamp, sampleA, sampleB, alternative='greater')

That said, I am not entirely convinced you need this at all. How about simply

def postprocessStats(testStatistic):
   ...some actions...
   return testStatistic

postprocessStats(scipy.stats.mstats.ks_twosamp(sampleA, sampleB, alternative='greater'))

?

I think this is easier to read and at the same time is more general.

edited May 23, 2017 at 12:11

CommunityBot

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answered Mar 27, 2013 at 8:24

NPE

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3 Comments

Ricky Robinson Over a year ago

Ha! The last solution is cool! As for **kwargs, when I don't specify it I guess it's just None and I can pass it as an argument with no side-effects, right?

NPE Over a year ago

@RickyRobinson: It's OK to specify no arguments when using **kwargs. You'll just get an empty dictionary, and everything will work as expected.

Rafael Barbosa Over a year ago

Note that in **kwargs (and *args), the names are just conventions. The important bit are the * and the **

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