The error range for the "duplicate argument in function definition" SyntaxError is too large:

$ cat x.py 
def f(a, b, c, d, e, f, g, a): pass
$ python x.py
  File "/home/cfbolz/projects/cpython/x.py", line 1
    def f(a, b, c, d, e, f, g, a): pass
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
SyntaxError: duplicate argument 'a' in function definition

I would expect only the second 'a' to be underlined.

I can try to fix this.

Thanks for the catch Carl!

> I can try to fix this.

Awesome, I will wait for the PR!

let's see whether I promised too much, I don't know CPython's symtable.c too well yet ;-). Will shout for help when I get stuck.

Anyway, here is a related bug, coming from the same symtable function symtable_add_def_helper, also with an imprecise error location:

$ cat x.py 
{i for i in range(5)
        if (j := 0)
            for j in range(5)}

$ ./python x.py 
  File "/home/cfbolz/projects/cpython/x.py", line 1
    {i for i in range(5)
    ^^^^^^^^^^^^^^^^^^^^
SyntaxError: comprehension inner loop cannot rebind assignment expression target 'j'

Don't worry, turns out it was a bit messier than I thought, so I prepared the PR. If you have some time, it would be great if you can take a quick look.

Oh no, I was about to open mine ;-)

bpo-46042-syntax-error-range-duplicate-argument?expand=1">https://github.com/python/cpython/compare/main...cfbolz:bpo-46042-syntax-error-range-duplicate-argument?expand=1

Basically equivalent, but I fixed the second bug too (would be very easy to add to yours)

ah, confused, seems you fixed them both too. will take a closer look!

New changeset 59435eea08d30796174552c0ca03c59b41adf8a5 by Pablo Galindo Salgado in branch 'main':
bpo-46042: Improve SyntaxError locations in the symbol table (GH-30059)
https://github.com/python/cpython/commit/59435eea08d30796174552c0ca03c59b41adf8a5

> Oh no, I was about to open mine ;-)

Sorry, Carl, I apologize. I hope it was not too disruptive to do the work. I was taking a look and I felt bad that the issue was probably messier than I thought and I didn't want you to have to iterate many times :(

Thanks a lot for helping review the PR and for pointing out the extra cases!!

New changeset 438817fdd5b731d486285d205bed2e78b655c0d6 by Miss Islington (bot) in branch '3.10':
bpo-46042: Improve SyntaxError locations in the symbol table (GH-30059) (GH-30064)
https://github.com/python/cpython/commit/438817fdd5b731d486285d205bed2e78b655c0d6

Oh, don't worry, it's all good! It got fixed and I learned something.