CODEWITHSUNDEEP
pythonargumentskeywordkeyword-argument
lbf_1994
lbf_1994

Reputation: 259

Use arguments of one function as arguments for other function

Suppose I have the following function

def f(x,y,**kwargs):
    if 'z' in kwargs:
        z = kwargs['z']
    else:
        z = 0
    print(x + y + z)

which takes two arguments and an optional keyword argument. I now want to get a function g that works just as f but for which the value of z is predetermined. Hence, I could do the following

def g(x,y):
    z = 3 
    f(x,y, z = 3)

But what can I do if I do not know the number of non-keyword arguments that f takes. I can get the list of these arguments by

args = inspect.getargspec(f)[0]

But, if I now define g as

g(args):
    z = 3
    f(args, z=z)

this of course does not work as only one mandatory argument is passed to f. How do I get around this? That is, if I have a function that takes keyword arguments, how do I define a second function exactly the same expect that the keyword arguments take predeterminde values?

Upvotes: 0

Views: 30

Answers (2)

Aran-Fey
Aran-Fey

Reputation: 43136

You have a few options here:

  1. Define g with varargs:

    def g(*args):
    return f(*args, z=3)

    Or, if you need keyword arguments as well:

    def g(*args, **kwargs):
    kwargs['z'] = 3
    return f(*args, **kwargs)

  2. Use functools.partial:

    import functools

g = functools.partial(f, z=3)

    See also this related question: Python Argument Binders.

Upvotes: 1

Ballack
Ballack

Reputation: 966

You can use functools.partial to achieve this

import functools
f = functools.partial(f, z=2)

# the following example is the usage of partial function f
x = f(1, 2)
y = f(1, 2, k=3)
z = f(1, 2, z=4)

Upvotes: 0

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