Beginner friendly error messages for missing self

[SurenNihalani]

Feature or enhancement

Proposal:

>>> class A:
...     def lol(a):
...         print(a)
...
>>> A().lol(1)
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    A().lol(1)
    ~~~~~~~^^^
TypeError: A.lol() takes 1 positional argument but 2 were given

I'd like to request a better experience for this use case.

Has this already been discussed elsewhere?

https://discuss.python.org/t/beginner-friendly-error-messages-for-missing-self-typeerror-a-lol-takes-1-positional-argument-but-2-were-given/107414

Links to previous discussion of this feature:

No response

Linked PRs

• gh-152315: Add a suggestion for self #152326

[lul-cas]

Can I work on this?
If the solution is just the error message I can improve it.

[lul-cas]

If it makes sense to implement, of course.

Could this be left to linters instead? I see value in warning about this for new users, but I’m not sure whether the language itself should own this responsibility.

[edvilme]

I really like the idea. However, I think it is important to keep in mind that self is only a naming convention, as the first argument represents the instance. Hence, I think we could say "Did you forget the instance parameter (e.g., self), in the function definition?"

Otherwise, it could be confusing to users (e.g., only adding the self parameter, adding it not on the first position, etc)

[SurenNihalani]

@lul-cas , same pinch. I made a PR before asking for permission. I'm new here. How do tasks get assigned?

@edvilme , I've posted a PR with proposed message.

[lul-cas]

@SurenNihalani no problem :)
I'm glad to help if needed.

[edvilme]

@lul-cas , same pinch. I made a PR before asking for permission. I'm new here. How do tasks get assigned?

@edvilme , I've posted a PR with proposed message.

Edit: thought i was tagged on both messages. Yes, left a comment on your PR with suggestion :)

[terryjreedy]

There was sufficient agreement on the discussion to do this. PyPy already adds a hint in a specific circumstance.