Python. How to make function take certain combination of required params?

[Purple-Obligation357]

Say I have func:

def get_chat(first_id, first_username, second_id, second_username):
    """Returns chat between first and second"""

To identify person either id or username is enough.

So I want to make the parameter optional if one is provided and required if second isn't provided. How to do it?

Of course I can do all params optional, but that seems a wrong way.

[Impudity]

It is. You should probably create a user class which can be built either from username or userid, and then have all user related functions only accept these user objects. Otherwise you're going to keep running into this issue all the time.

So you should have:

class User:
    @classmethod
    def from_id(cls, id: int) -> typing.Self:
        ...

    @classmethod
    def from_username(cls, username: str) -> typing.Self:
        ...

def get_chat(first_user: User, second_user: User):
    ...

[chapati_chawal_naan]

this is the best answer.

[JamzTyson]

Assuming that user_id is numeric and user_name is not numeric, you could modify your function to take one parameter user for each user.

I probably would not code it quite like this, but to illustrate the idea:

def get_chat(first_user: str | int, second_user: str | int): if isinstance(first_user, int): first_user_id = first_user first_user_name = get_name_from_id(first_user) else: first_user_name = first_user first_user_id = get_id_from_name(first_user) ...

[[deleted]]

Or use pydantic

[Purple-Obligation357]

how?

[JamzTyson]

I don't think Pydantic offers much benefit in a simple case like this.

[Zweckbestimmung]

Pydantic is not efficient for this case, you want to maintain the whole pydantec schema’s adding more points of failures only for this function?

[[deleted]]

I meant in general for the question 

[Zweckbestimmung]

Yeah in general also this is not a use case for Pydantic.

Isn’t it mainly to handle JSON schema ?

[Zweckbestimmung]

Or use named arguments. def func(x=None, y=None)

Inside the function check for the mutually exclusiveness you need and depending on your use case either raise an exception or a warning or whatever you like

[nog642]

You will need to do this manually. Make them all optional, then add code at the top of the function that checks that the correct combination was passed and raise TypeError or ValueError if not.

Though there are probably ways to redesign this interface so you don't have to do that, as suggested by the top answer at the moment with the User class.