How to check whether optional function parameter is set

Question

Is there an easy way in Python to check whether the value of an optional parameter comes from its default value, or because the user has set it explicitly at the function ca

Answer 1

The following function decorator, explicit_checker, makes a set of parameter names of all the parameters given explicitly. It adds the result as an extra parameter (explicit_params) to the function. Just do 'a' in explicit_params to check if parameter a is given explicitly.

def explicit_checker(f):
    varnames = f.func_code.co_varnames
    def wrapper(*a, **kw):
        kw['explicit_params'] = set(list(varnames[:len(a)]) + kw.keys())
        return f(*a, **kw)
    return wrapper

@explicit_checker
def my_function(a, b=0, c=1, explicit_params=None):
    print a, b, c, explicit_params
    if 'b' in explicit_params:
        pass # Do whatever you want


my_function(1)
my_function(1, 0)
my_function(1, c=1)