Calling an arbitrary function with the right arguments

Steven D'Aprano steve-REMOVE-THIS at cybersource.com.au
Mon Sep 27 06:10:46 CEST 2010


On Mon, 27 Sep 2010 03:41:13 +0000, John O'Hagan wrote:

> How to call a function with the right arguments without knowing in
> advance which function? For example:

> 
> import random
> 
> def f1():
>     pass
> 
> def f2(foo):
>     pass
> 
> def f3(foo, bar):
>     pass
> 
> foo=random.choice((1,2,3))
> bar=random.choice((1,2,3))
> 
> myfunc=random.choice((f1, f2, f3))
> 
> How to call myfunc with the right arguments? 


If f1, f2 and f3 require different arguments, it's not sensible to expect 
them to be interchangeable. The right way to do this is to re-write the 
functions so they all have the same call signature (even if that is just 
to ignore unnecessary arguments). Or wrap the functions (perhaps using 
functools.partial) so they don't need the extra args.

f3 = lambda f=f3: f(foo, bar)
f2 = lambda f=f2: f(foo)



Either way, there's a reason you never see callback functions that accept 
arbitrary arguments. They always have a standard, fixed argument list.



-- 
Steven



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