Standard Python wrapper to turn f(x) into f(*x)?

Question

I keep coming across use cases for the following wrapper:

def asterisk(fn):
   def retfn(x):
      return fn(*x)
   return retfn

Is there something in the standard Python 2 library that already does this? I had a look in functools, but couldn't find anything.

For context, here is a recent use case:

print map(asterisk(operator.sub), [[-20, 20], [-20, 20], [32, 32]])

Answer 1

To provide this:

print map(asterisk(operator.sub), [[-20, 20], [-20, 20], [32, 32]])

You should use

from itertools import starmap
print starmap(operator.sub, [[-20, 20], [-20, 20], [32, 32]])

P.S. As far as I know, there is no built-in functions for such functionality in Python. Some time ago, I talked in Python mailing list about lack of "apply" functionality, which is more "general" questions. I think, something like operator.apply(f, args) will be good for many cases. This functional representation for function application can also except argument about arguments passing model.

Answer 2

While starmap is a good solution for some cases, another option here, which I feel is far more readable in this case, is to use a list comprehension instead:

[x - y for x, y in [[-20, 20], [-20, 20], [32, 32]]

I would recommend that you use a list comprehension (or generator expression) as soon as you find yourself using the operator module or lambdas, as it will result in far more readable (and often faster) code.