Call Functions with Dynamic Parameters in Python

March 27, 2022

When I was studying my colleague’s brilliant coding work, I noticed a very interesting implementation on calling functions with dynamic parameters in python.

import inspect

# May come from anywhere such as HTTP / RPC calls, environment variables
# where the format of params_from_anywhere is uncontrolled
params_from_anywhere = {
    "a": "a value",
    "b": "b value",
    "c": "c value",
    "d": "d value",
    "e": "e value",
    "f": "f value",
    "g": "g value",
    "h": "h value",
    "i": "i value",
}


def fn_i_want_to_call(*, c=None, e=None, g=None, i=None, j=None):
    print(c)
    print(e)
    print(g)
    print(i)
    print(j)


def call_fn_with_dynamic_params(fn, params):
    all_kwargs = inspect.getfullargspec(fn).kwonlyargs
    required_kwargs = {k: v for k, v in params.items() if k in all_kwargs}
    fn_i_want_to_call(**required_kwargs)


call_fn_with_dynamic_params(fn_i_want_to_call, params_from_anywhere)

# output:
# c value
# e value
# g value
# i value
# None

It’s very interesting. It’s not calling fn_i_want_to_call function with specifying the parameters explicitly. Instead, it calls inspect.getfullargspec(fn).kwonlyargs to find out what the parameters are required in fn_i_want_to_call function and then dynamically map the parameters from a dictionary.

I feel it’s an interesting trick which can reduce the dumb manual parameter extractions from dictionary, so I made this demo code snippet and share to you all.