Can one partially apply the second argument of a function that takes no keyword arguments?

beoliver picture beoliver · Jun 24, 2012 · Viewed 17.4k times · Source

Take for example the python built in pow() function.

xs = [1,2,3,4,5,6,7,8]

from functools import partial

list(map(partial(pow,2),xs))

>>> [2, 4, 8, 16, 32, 128, 256]

but how would I raise the xs to the power of 2?

to get [1, 4, 9, 16, 25, 49, 64]

list(map(partial(pow,y=2),xs))

TypeError: pow() takes no keyword arguments

I know list comprehensions would be easier.

Answer

Eric picture Eric · Jun 24, 2012

No

According to the documentation, partial cannot do this (emphasis my own):

partial.args

The leftmost positional arguments that will be prepended to the positional arguments


You could always just "fix" pow to have keyword args:

_pow = pow
pow = lambda x, y: _pow(x, y)