[Python-ideas] Re: On function signature mismatch, include candidate function in traceback

21 Apr 2021

      Hah, should have put more effort in my research then. And so recent too.
Well, it is not something easy to search for.

I read the other thread, and I am inclined to agree with Paul. Whether 
or not the execution enters the function (as in: new entry in the call 
stack) during setup is really an implementation detail.
For the very same reason, I also see why the CPython devs don't want to 
include a fake extra stack layer.

Still, personally, I think that during the checking of the function 
arguments, execution is logically closer to the function than the point 
where it was called. I also think that the stack part of the traceback 
*is* the right place to display this information.

I'd also be fine with an extended exception message though.

In the end, I think this is a trivial improvement. (Trivial as in 'no 
adverse side effects', not trivial to implement).
Regardless if it has affected many users in the past or not (I'd say it 
did!).

I am anything but an authoritative figure on the matter, so just 
consider this a firm +1 from another user.

Cheers
Pol

On 2021-04-21 01:20, Paul Sokolovsky wrote:
...
Hello,
On Tue, 20 Apr 2021 18:23:15 -0000
"Pol Welter"  wrote:
...
Consider the following snippet:
```
def foo(a, b):
     pass
foo(1, 2, 3)
```
We all know what will happen.
```
   File "<stdin>", line 4, in <module>
     foo(1, 2, 3)
TypeError: foo() takes 2 positional arguments but 3 were given
```
Would it be reasonable to include the line number for the function
`foo()` that it resolved the call to? I.e. 'File "<stdin>", line 1,
in foo'.
There are situations (e.g. monkey patch) where this is not obvious.
Would be great detail to include that in the traceback, I think.
That was reported some time ago:
https://groups.google.com/g/dev-python/c/xdcpSJN17QQ
https://groups.google.com/g/python-ideas/c/3jEZ9F-oUr0
Just as you, I had hard time to believe that wasn't fixed over 30 years
of CPython history.
I fixed that in my Python dialect, https://github.com/pfalcon/pycopy ,
and enjoyed it thoroughly on multiple occasions since then. For the
snippet above (put in a file):
Traceback (most recent call last):
   File "ex.py", line 4, in <module>
   File "ex.py", line 2, in foo
TypeError: foo() takes 2 positional arguments but 3 were given