How to programmatically determine if the default parameter value was used?

Given a function:

def foo(num = 42, bar = 100):
    print("num:", num)

How might I add code to foo to learn if foo was invoked with no argument for the num and/or bar parameters?

You might use decorator for unveiling what arguments were passed following way

def show_arguments(func):
    def wrapper(*args, **kwargs):
        print('Positional arguments', args)
        print('Keyword arguments', kwargs)
        return func(*args, **kwargs)
    return wrapper


@show_arguments
def foo(num = 42, bar = 100):
    print("num:", num)


foo()
foo(1)
foo(num=1)
foo(1,bar=1)
foo(num=1,bar=1)

gives output

Positional arguments ()
Keyword arguments {}
num: 42
Positional arguments (1,)
Keyword arguments {}
num: 1
Positional arguments ()
Keyword arguments {'num': 1}
num: 1
Positional arguments (1,)
Keyword arguments {'bar': 1}
num: 1
Positional arguments ()
Keyword arguments {'num': 1, 'bar': 1}
num: 1

Observe that function in python are 1st class citizens.