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Description
Feature or enhancement
We propose a few improvements and fixes toPEP-657, namely:
- Support underlining errors that span across multiple lines instead of only showing the first line
- Use caret anchors for function calls as well
- Fix bracket/binary op heuristic in the caret anchor computation function
Pitch
We already implemented these items in PyTorch here:pytorch/pytorch#104676. We're seeing if these may be worth adding to CPython.
Rationale for 1
Multi-line expressions can negate the utility ofPEP-657, for example:
really_long_expr_1=1really_long_expr_2=2really_long_expr_3=0really_long_expr_4=4y= ( (really_long_expr_1+really_long_expr_2 )/really_long_expr_2/really_long_expr_3)
Current traceback:
Traceback (most recent call last): File "/scratch/williamwen/work/pytorch/playground5.py", line 25, in <module> (ZeroDivisionError: float division by zeroBetter traceback:
Traceback (most recent call last): File "/scratch/williamwen/work/pytorch/playground5.py", line 25, in <module> ( ~ really_long_expr_1 + ~~~~~~~~~~~~~~~~~~~~ really_long_expr_2 ~~~~~~~~~~~~~~~~~~ ) / ~~^ really_long_expr_2 / ~~~~~~~~~~~~~~~~~~ZeroDivisionError: float division by zeroRationale for 2
Helpful for identifying function calls that cause errors in chained function calls. We may as well do it since we're already doing it for subscripts. For example:
deff1(x1):deff2(x2):raiseRuntimeError()returnf2y=f1(1)(2)(3)
Current traceback:
Traceback (most recent call last): File "/scratch/williamwen/work/pytorch/playground5.py", line 22, in <module> y = f1(1)(2)(3) ^^^^^^^^ File "/scratch/williamwen/work/pytorch/playground5.py", line 6, in f2 raise RuntimeError()RuntimeErrorBetter traceback:
Traceback (most recent call last): File "/scratch/williamwen/work/pytorch/playground5.py", line 22, in <module> y = f1(1)(2)(3) ~~~~~^^^ File "/scratch/williamwen/work/pytorch/playground5.py", line 6, in f2 raise RuntimeError()RuntimeErrorRationale for 3
The binary op anchors are computed by taking the next non-space character after the left subexpression. This is incorrect in some simple cases:
x = (3) / 0 ~~^~~~~ZeroDivisionError: division by zeroWe should expect
x = (3) / 0 ~~~~^~~ZeroDivisionError: division by zeroThe fix is that we should continue advancing the anchor until we find a non-space character that is also not in)\# (for\#, we should move the anchor to the next line).
Subscript has a similar issue as well. We should continue advancing the left anchor until we find[, and the right anchor should be the end of the entire subscript expression.
cc@pablogsal@isidentical@ammaraskar@iritkatriel@ezyang
Linked PRs
- gh-106922: Fix error location for constructs with spaces and parentheses #108959
- [3.12] gh-106922: Fix error location for constructs with spaces and parentheses (GH-108959) #109147
- [3.11] gh-106922: Fix error location for constructs with spaces and parentheses (GH-108959) #109148
- gh-106922: Support multi-line error locations in traceback #109589
- gh-106922: Support multi-line error locations in traceback (attempt 2) #112097