traceback: add `recent_first` and `show_lines` parameters

[methane]

Feature or enhancement

Proposal:

traceback.print_exception() and other APIs showing traceback is optimized for developers looking console:

• It uses "most recent call last" order and print exception later.
• It shows source code lines. It makes the traceback huge when using large library like sqlalchemy.

On the other hand, Python applications would send traceback to observability backends like DataDog, New Relic, Grafana Loki, etc...
In such cases, "most recent first" order and shorter traceback without source are preferred because most other languages uses "most recent first" order and no source.

stdlib traceback should provide shorter and "most recent first" traceback format.

source:

import traceback

def f1():
    return 1 / 0

def f2():
    return f1()

try:
    f2()
except ZeroDivisionError as e:
    print("# default format")
    traceback.print_exception(e)

    print()
    print("# show_lines=False")
    traceback.print_exception(e, show_lines=False)

    print()
    print("# show_lines=False, recent_first=True")
    traceback.print_exception(e, show_lines=False, recent_first=True)

output:

# default format
Traceback (most recent call last):
  File "/Users/inada-n/work/python/cpython/tb_demo.py", line 10, in <module>
    f2()
    ~~^^
  File "/Users/inada-n/work/python/cpython/tb_demo.py", line 7, in f2
    return f1()
  File "/Users/inada-n/work/python/cpython/tb_demo.py", line 4, in f1
    return 1 / 0
           ~~^~~
ZeroDivisionError: division by zero

# show_lines=False
Traceback (most recent call last):
  File "/Users/inada-n/work/python/cpython/tb_demo.py", line 10, in <module>
  File "/Users/inada-n/work/python/cpython/tb_demo.py", line 7, in f2
  File "/Users/inada-n/work/python/cpython/tb_demo.py", line 4, in f1
ZeroDivisionError: division by zero

# show_lines=False, recent_first=True
ZeroDivisionError: division by zero
Traceback (most recent call first):
  File "/Users/inada-n/work/python/cpython/tb_demo.py", line 4, in f1
  File "/Users/inada-n/work/python/cpython/tb_demo.py", line 7, in f2
  File "/Users/inada-n/work/python/cpython/tb_demo.py", line 10, in <module>

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/shorter-and-reversed-format-for-traceback/51139

Linked PRs

• gh-135751: traceback: add recent_first and show_lines parameter #135752

[iritkatriel]

show_lines is confusing. I think you mean something like show_sourcecode.

[methane]

@iritkatriel it is discussed in the discuss.python.org thread.

For consisntency with .line, lookup_lines=, and show_group=, I decide to use show_lines.

https://discuss.python.org/t/shorter-and-reversed-format-for-traceback/51139/11

[iritkatriel]

Thanks, I hadn't seen that thread before. Not many people follow the ideas forum. I think the API design should be discussed in the development section as well. API design is important and one we merge this we are committed to maintaining it forever.