Separating **kwargs for different functions

Question

Given a higher order function that takes multiple functions as arguments, how could that function pass key word arguments to the function arguments?

example

def eat(food='eggs', how_much=1):
    print(food * how_much)


def parrot_is(state='dead'):
    print("This parrot is %s." % state)


def skit(*lines, **kwargs):
    for line in lines:
        line(**kwargs)

skit(eat, parrot_is)  # eggs \n This parrot is dead.
skit(eat, parrot_is, food='spam', how_much=50, state='an ex-parrot') # error

state is not a keyword arg of eat so how can skit only pass keyword args relevant the function that it is calling?

Answer 1

You can filter the kwargs dictionary based on func_code.co_varnames (in python 2) of a function:

def skit(*lines, **kwargs):
    for line in lines:
        line(**{key: value for key, value in kwargs.iteritems() 
                if key in line.func_code.co_varnames})

In python 3, __code__ should be used instead of func_code. So the function will be:

def skit(*lines, **kwargs):
    for line in lines:
        line(**{key: value for key, value in kwargs.iteritems() 
                if key in line.__code__.co_varnames})

Also see: Can you list the keyword arguments a function receives?

Answer 2

If you add **kwargs to all of the definitions, you can pass the whole lot:

def eat(food='eggs', how_much=1, **kwargs):
    print(food * how_much)


def parrot_is(state='dead', **kwargs):
    print("This parrot is %s." % state)


def skit(*lines, **kwargs):
    for line in lines:
        line(**kwargs)

Anything in **kwargs that isn't also an explicit keyword argument will just get left in kwargs and ignored by e.g. eat.

Example:

>>> skit(eat, parrot_is, food='spam', how_much=50, state='an ex-parrot')
spamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspamspam
This parrot is an ex-parrot.