Give function defaults arguments from a dictionary in Python

Question

Let's imagine I have a dict :

d = {'a': 3, 'b':4}

I want to create a function f that does the exact same thing than this function :

def f(x, a=d['a'], b=d['b']):
  print(x, a, b)

(Not necessarily print, but do some stuff with the variable and calling directly from their name).

But I would like to create this function directly from the dict, that is to say, I would like to have something that look likes

def f(x, **d=d):
  print(x, a, b)

and that behaves like the previously defined function. The idea is that I have a large dictionary that contains defaults values for arguments of my function, and I would like not to have to do

def f(a= d['a'], b = d['b'] ...)

I don't know if it's possible at all in python. Any insight is appreciated !

Edit : The idea is to be able to call f(5, a=3). Edit2 : The question is not about passing arguments stored in a dict to a function but to define a function whose arguments names and defaults values are stored in a dict.

Answer 1

You cannot achieve this at function definition because Python determines the scope of a function statically. Although, it is possible to write a decorator to add in default keyword arguments.

from functools import wraps

def kwargs_decorator(dict_kwargs):
    def wrapper(f):
        @wraps(f)
        def inner_wrapper(*args, **kwargs):
            new_kwargs = {**dict_kwargs, **kwargs}
            return f(*args, **new_kwargs)
        return inner_wrapper
    return wrapper

Usage

@kwargs_decorator({'bar': 1})
def foo(**kwargs):
    print(kwargs['bar'])

foo() # prints 1

Or alternatively if you know the variable names but not their default values...

@kwargs_decorator({'bar': 1})
def foo(bar):
    print(bar)

foo() # prints 1

Caveat

The above can be used, by example, to dynamically generate multiple functions with different default arguments. Although, if the parameters you want to pass are the same for every function, it would be simpler and more idiomatic to simply pass in a dict of parameters.