✨ Add support for standard tracebacks via the env TYPER_STANDARD_TRACEBACK

[colin-nolan]

This PR allows standard tracebacks to be enabled using the environment variable: TYPER_STANDARD_TRACEBACK.

The work is a follow up to the discussion with @svlandeg: #1284.

The existing environment variable _TYPER_STANDARD_TRACEBACK is retained but referred to as "deprecated" because:

• It is non-standard for an advertised env to start with an underscore.
• Environment variables that start with an underscore have been observed as causing issues in some execution environments (e.g. with AWS Lambda).

Manual testing with:

import typer

def main():
    raise Exception("Hello World")

if __name__ == "__main__":
    typer.run(main)

Produces expected results:

$ python will-fail.py 
╭───────────────────────────────────────── Traceback (most recent call last) ─────────────────────────────────────────╮
│ /Users/cnolan/repositories/typer/will-fail.py:5 in main                                                             │
│                                                                                                                     │
│   2 import typer                                                                                                    │
│   3                                                                                                                 │
│   4 def main():                                                                                                     │
│ ❱ 5 │   raise Exception("Hello World")                                                                              │
│   6                                                                                                                 │
│   7 if __name__ == "__main__":                                                                                      │
│   8 │   typer.run(main)                                                                                             │
╰─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
Exception: Hello World

$ TYPER_STANDARD_TRACEBACK=1 python will-fail.py 
Traceback (most recent call last):
  File "/Users/cnolan/repositories/typer/will-fail.py", line 8, in <module>
    typer.run(main)
    ~~~~~~~~~^^^^^^
  File "/Users/cnolan/repositories/typer/typer/main.py", line 1073, in run
    app()
    ~~~^^
  File "/Users/cnolan/repositories/typer/typer/main.py", line 332, in __call__
    raise e
  File "/Users/cnolan/repositories/typer/typer/main.py", line 315, in __call__
    return get_command(self)(*args, **kwargs)
           ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/Users/cnolan/repositories/typer/.venv/lib/python3.13/site-packages/click/core.py", line 1442, in __call__
    return self.main(*args, **kwargs)
           ~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/Users/cnolan/repositories/typer/typer/core.py", line 700, in main
    return _main(
        self,
    ...<6 lines>...
        **extra,
    )
  File "/Users/cnolan/repositories/typer/typer/core.py", line 193, in _main
    rv = self.invoke(ctx)
  File "/Users/cnolan/repositories/typer/.venv/lib/python3.13/site-packages/click/core.py", line 1226, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/cnolan/repositories/typer/.venv/lib/python3.13/site-packages/click/core.py", line 794, in invoke
    return callback(*args, **kwargs)
  File "/Users/cnolan/repositories/typer/typer/main.py", line 692, in wrapper
    return callback(**use_params)
  File "/Users/cnolan/repositories/typer/will-fail.py", line 5, in main
    raise Exception("Hello World")
Exception: Hello World

$ _TYPER_STANDARD_TRACEBACK=1 python will-fail.py 
Traceback (most recent call last):
  File "/Users/cnolan/repositories/typer/will-fail.py", line 8, in <module>
    typer.run(main)
    ~~~~~~~~~^^^^^^
  File "/Users/cnolan/repositories/typer/typer/main.py", line 1073, in run
    app()
    ~~~^^
  File "/Users/cnolan/repositories/typer/typer/main.py", line 332, in __call__
    raise e
  File "/Users/cnolan/repositories/typer/typer/main.py", line 315, in __call__
    return get_command(self)(*args, **kwargs)
           ~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/Users/cnolan/repositories/typer/.venv/lib/python3.13/site-packages/click/core.py", line 1442, in __call__
    return self.main(*args, **kwargs)
           ~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/Users/cnolan/repositories/typer/typer/core.py", line 700, in main
    return _main(
        self,
    ...<6 lines>...
        **extra,
    )
  File "/Users/cnolan/repositories/typer/typer/core.py", line 193, in _main
    rv = self.invoke(ctx)
  File "/Users/cnolan/repositories/typer/.venv/lib/python3.13/site-packages/click/core.py", line 1226, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/cnolan/repositories/typer/.venv/lib/python3.13/site-packages/click/core.py", line 794, in invoke
    return callback(*args, **kwargs)
  File "/Users/cnolan/repositories/typer/typer/main.py", line 692, in wrapper
    return callback(**use_params)
  File "/Users/cnolan/repositories/typer/will-fail.py", line 5, in main
    raise Exception("Hello World")
Exception: Hello World

[github-actions]

📝 Docs preview for commit b77ece1 at: https://11faf57b.typertiangolo.pages.dev

Modified Pages

• https://11faf57b.typertiangolo.pages.dev/tutorial/exceptions/ - (before)

[svlandeg]

As discussed, this PR adds the option to set an env var TYPER_STANDARD_TRACEBACK while still supporting the old var _TYPER_STANDARD_TRACEBACK too. We need to support both because we don't want to break existing workflows, but that does complicate the code slightly. I think that's an acceptable trade-off to ensure this variable can be properly set in AWS Lambda etc.

[svlandeg]

It's worth pointing out that this implementation introduces a priority: if both of these variables are set in the environment, then only TYPER_STANDARD_TRACEBACK will be retrieved & used. I think that's fine though, and it would be an extreme niche case if TYPER_STANDARD_TRACEBACK was set to 0 for instance and _TYPER_STANDARD_TRACEBACK to 1 🤷‍♀️

[colin-nolan]

I had the same thought. However, I noticed that it's not possible to turn this functionality off by setting the env to any non-empty value:

typer/typer/main.py

Lines 68 to 73 in 0b6a405

	standard_traceback = os.getenv("_TYPER_STANDARD_TRACEBACK")
	if (
	standard_traceback
	or not exception_config
	or not exception_config.pretty_exceptions_enable
	):

(where standard_traceback = "0" -> truthy).

The consequence is that a disagreement can only happen when one variable is set to empty string, and another set to a value. In this case, did the user mean empty string to signal off, or just "unset"?

I think the new env overriding the legacy is acceptable but it's debatable.

I considered changing to support 0 -> off but I didn't want to increase the scope (and it could be argued that it is a breaking change - but it probably more of a bug fix).

[svlandeg]

I will leave this PR for a final review by Tiangolo 🙏