Let's say I have the following function:
def add(x, y):
return x+y
I would like to bind x=2 and y=2 to the function but not actually call it. What is the correct way to do this? I've done this sometimes with add_bound=lambda: add(2,3), but I'm wondering if this is the 'pythonic' approach or there is another way to do it (perhaps binding certain arguments, and then passing other arguments later.
Often this will be done with a decorator. Here is a general example:
add = lambda x,y: x+y
def wrap(outer_func, *outer_args, **outer_kwargs):
def inner_func(*inner_args, **inner_kwargs):
args = list(outer_args) + list(inner_args)
kwargs = {**outer_kwargs, **inner_kwargs}
return outer_func(*args, **kwargs)
return inner_func
In this case you can do things such as the following:
# pass both at once
>>> x=wrap(add,2,3)
>>> x()
5
# pass one at binding, second at call
>>> x=wrap(add,2)
>>> x(3)
5
# pass both when called
>>> x=wrap(add)
>>> x(2,3)
5
Note that the above is very similar to functools.partial:
The partial() is used for partial function application which “freezes” some portion of a function’s arguments and/or keywords resulting in a new object with a simplified signature. For example, partial() can be used to create a callable that behaves like the int() function where the base argument defaults to two:
from functools import partial
basetwo = partial(int, base=2)
basetwo.__doc__ = 'Convert base 2 string to an int.'
basetwo('10010')
18
def add(x=2, y=2):
return x+y
