Python function make parameter mandatory if another parameter is passed

Question

I have a function in Python as

def myfunc(a, b=None, c=None):
    my code here

Is there a way to ensure that if the user passes the value of the parameter b it is necessary to pass the parameter c to myfunc?

score 1 · Accepted Answer · answered Nov 02 '21 at 06:13

1

You can write a simple if condition in your function. See the code below:

def myfunc(a, b=None, c=None):
    if c is not None and b is None:
        raise ValueError("Value of b must be passed if value of c is passed")
    your code here

answered Nov 02 '21 at 06:13

betelgeuse

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what if user has provided `None` as third argument, this will fail – sahasrara62 Nov 02 '21 at 06:23
The assumption here is that passing `None` is equivalent to not passing anything since `None` is the default value here. – betelgeuse Nov 02 '21 at 06:26
None is assumed as default value not no value is passed – sahasrara62 Nov 02 '21 at 06:43

score 1 · Answer 2 · answered Nov 02 '21 at 06:13

1

Not in any built in way. Check it yourself:

def myfunc(a, b=None, c=None):
    if b is not None and c is None:
        raise ValueError("Invalid arguments")
    # ...

answered Nov 02 '21 at 06:13

Ouroborus

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what if user has provided `None` as third argument, this will fail – sahasrara62 Nov 02 '21 at 06:22
@sahasrara62 If you supply a value that is the same as a default value, it's assumed you wanted whatever behavior the default value implies. – Ouroborus Nov 02 '21 at 06:34
it can be one of the case where c value passed in `None` in that sense for me atleast this solution doesn't make any sense – sahasrara62 Nov 02 '21 at 06:42
@sahasrara62 For a python function defined as `def func(a=None)`, calling it with either `func()`, `func(None)`, or `func(a=None)`, are all expected to have the same behavior. – Ouroborus Nov 02 '21 at 07:02

Python function make parameter mandatory if another parameter is passed

2 Answers2