How to *not* set sys.excepthook?

[charmoniumQ]

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Example Code

import typer
import rich.traceback
rich.traceback.install(
    show_locals=False,
    # other awesome configs here, not just show_locals=False
    suppress=[
        # e.g.,
        #numpy.__file__,
    ],
)

app = typer.Typer()

@app.command()
def main():
    x = 2
    raise ValueError()

app()
# shows traceback WITH locals, even though I installed rich without locals.
# Yes, I know pretty_exceptions_show_locals exists, but locals are just an easily-demo-able representative for all of my Rich traceback configuration

Description

It seems that Typer overwrites the sys.excepthook here and it's impossible to disable that functionality.

This is important because I have a nice rich.traceback configuration that suppresses stackframes, customizes width, etc. Typer calls rich.traceback, but lacks these customization options I want set.

Even passing pretty_exceptions_short=False still sets the sys.excepthook to the (ugly) stdlib excepthook here. Arguably, that flag or perhaps a new flag should just avoid setting sys.excepthook on line 318.

I can implement this in a PR, but I was wondering if it would be worth it for others, or if that is a feature that would be accepted.

rich_markup_mode=None is not right either; it disables all of Rich markup; I just want Typer to not overwrite the sys.excepthook.

Operating System

Linux

Operating System Details

NixOS

Typer Version

0.12.3

Python Version

Python 3.12.5

Additional Context

No response

[djachenko]

I've done some debugging and found I can capture sys.excepthook before app() and put it back at app callback, but it's still quite dirty hack.

[DhruvalAnandkar]

Hi @charmoniumQ, and thanks for the debugging, @djachenko - that capture/restore trick makes sense as a workaround, and it actually points at exactly what's going on under the hood.

I dug into Typer's source (main.py) to see exactly what's happening. Two things combine to cause this:

1st---> Typer only saves the ORIGINAL sys.excepthook once at import time - literally the first time import typer runs anywhere in your process not when app() is called.
2nd---> Every time you call app() the Typer unconditionally overwrites sys.excepthook with its own handler so that handler only falls back to the saved original when pretty_exceptions_enable=False.

Put those together and your example has the ordering backwards: import typer runs first so Typer captures the plain stdlib hook as its fallback - before your rich.traceback.install() call ever runs. That's exactly why you saw the stdlib traceback instead of your Rich config even when trying to disable Typer's own renderer.

The fix is to flip the order so Typer's snapshot captures your Rich hook instead:

import rich.traceback

rich.traceback.install(
    show_locals=False,
    suppress=[
        # your config here
    ],
)

import typer # import typer AFTER installing your rich hook

app = typer.Typer(pretty_exceptions_enable=False)

@app.command()
def main():
    x = 2
    raise ValueError()

if __name__ == "__main__":
    app()

With pretty_exceptions_enable=False, Typer's hook falls straight through to the "original" hook it saved - which is now your fully-configured Rich installer, locals/suppress/width and all, instead of stdlib or Typer's own version.

One caveat worth knowing: this only works if nothing else in your dependency chain imports typer before your script does. If some other library imports it first, the snapshot happens then instead, and you'd need @djachenko's capture/restore approach as a fallback for that case.

Also worth linking: #508 is tracking this exact friction as an open issue, if you want a supported programmatic override down the line rather than relying on import order.

Hope this gets you the traceback config you were after! Let me know if the reordering works on your end. (And if this clears things up, I'd really appreciate it if you could mark this as the answer! )