Function with many arguments, with some default values

[medatib531]

I want to create a function that takes multiple arguments (about 20).
However some of them might default to some pre-selected values.

I was thinking of organizing the arguments into dictionaries to make the code more readable, but how can I get a function with a dictionary as input to default to a value when the respective dictionary entry is not passed?

[ndc85430]

Why do you have a function that needs so many things? That's a sign that it's probably doing too much.

[deanhystad]

Have you tried using keyword arguments? I find them easy to read

def many_arg_func(
        required_arg: str,  # No default, so must supply value
        arg1: int = 42, # Has a default, you can skip
        mebbe_a_string: str = None, # Can skip this even if not a str
        a_float: float = 1.234,
        a_tuple: tuple = (),
        even_a_dict: dict = {}):
    print(arg1)
    print(mebbe_a_string)
    print(a_float)
    print(a_tuple)
    print(even_a_dict)


print('many_arg_func')
many_arg_func(
    required_arg = 'This is required',
    a_tuple = (1, 2, 3, 4),
    even_a_dict = {'key': 'value', 'another key': 'another value'})

def func_with_optional_args(
        req: str,
        opt1: int = None,   # Will provide default later
        opt2: float = None,
        opt3: tuple = None):
    # Provide some defaults
    if opt1 is None: opt1 = 42
    if opt2 is None: opt2 = 1.234
    if opt3 is None: opt3 = (1, 2, 3, 4)
    print(req)
    print(opt1)
    print(opt2)
    print(opt3)

print('\nfunc_with_optional_args')
func_with_optional_args(
    req = 'required arg',
    opt3 = ('one', 'two', 'three', 'four'))


def many_arg_func_helper(
    # I fill in some of the args and call many_arg_func
    arg1: int = None,
    a_float: float = None):
    many_arg_func(
        required_arg = 'Required',
        arg1 = arg1,
        a_float = a_float,
        a_tuple = ('something',),
        even_a_dict = {'arg1': arg1, 'a_float': a_float})

print('\nmany_arg_func with helper')
many_arg_func_helper()

This is the output when I run the script.

Output:
many_arg_func
42
None
1.234
(1, 2, 3, 4)
{'key': 'value', 'another key': 'another value'}

func_with_optional_args
required arg
42
1.234
('one', 'two', 'three', 'four')

many_arg_func with helper
None
None
None
('something',)
{'arg1': None, 'a_float': None}

Notice the output when the helper function is used. arg_1 and a_float are both None even though the many_arg_func provides a default integer and float value. Why are they None? The reason is that default values in the argument list are only used when no value is provided. When many_arg_func_helper is called it provides arg_1 and a_float with a default value of None. When many_arg_func_helper calls "many_arg_func the None values are passed along. For this reason I only use None for default values and provide default values inside the function body.

[medatib531]

Think this works for me, thanks!