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Traceback
=========
Rich can render Python tracebacks with syntax highlighting and formatting. Rich tracebacks are easier to read and show more code than standard Python tracebacks.
To see an example of a Rich traceback, running the following command::
python -m rich.traceback
Printing tracebacks
-------------------
The :meth:`~rich.console.Console.print_exception` method will print a traceback for the current exception being handled. Here's an example::
from rich.console import Console
console = Console()
try:
do_something()
except Exception:
console.print_exception(show_locals=True)
The ``show_locals=True`` parameter causes Rich to display the value of local variables for each frame of the traceback.
See `exception.py <https://github.com/willmcgugan/rich/blob/master/examples/exception.py>`_ for a larger example.
Traceback Handler
-----------------
Rich can be installed as the default traceback handler so that all uncaught exceptions will be rendered with highlighting. Here's how::
from rich.traceback import install
install(show_locals=True)
There are a few options to configure the traceback handler, see :func:`~rich.traceback.install` for details.
Automatic Traceback Handler
^^^^^^^^^^^^^^^^^^^^^^^^^^^
In some cases you may want to have the traceback handler installed automatically without having to worry about importing the code in your module. You can do that by modifying the `sitecustomize.py` in your virtual environment. Typically it would be located in your virtual environment path, underneath the `site-packages` folder, something like this::
./.venv/lib/python3.9/site-packages/sitecustomize.py
In most cases this file will not exist. If it doesn't exist, you can create it by::
$ touch .venv/lib/python3.9/site-packages/sitecustomize.py
Add the following code to the file::
from rich.traceback import install
install(show_locals=True)
At this point, the traceback will be installed for any code that is run within the virtual environment.
.. note::
If you plan on sharing your code, it is probably best to include the traceback install in your main entry point module.
Suppressing Frames
------------------
If you are working with a framework (click, django etc), you may only be interested in seeing the code from your own application within the traceback. You can exclude framework code by setting the `suppress` argument on `Traceback`, `install`, `Console.print_exception`, and `RichHandler`, which should be a list of modules or str paths.
Here's how you would exclude `click <https://click.palletsprojects.com/en/8.0.x/>`_ from Rich exceptions::
import click
from rich.traceback import install
install(suppress=[click])
Suppressed frames will show the line and file only, without any code.
Max Frames
----------
A recursion error can generate very large tracebacks that take a while to render and contain a lot of repetitive frames. Rich guards against this with a `max_frames` argument, which defaults to 100. If a traceback contains more than 100 frames then only the first 50, and last 50 will be shown. You can disable this feature by setting `max_frames` to 0.
Here's an example of printing a recursive error::
from rich.console import Console
def foo(n):
return bar(n)
def bar(n):
return foo(n)
console = Console()
try:
foo(1)
except Exception:
console.print_exception(max_frames=20)
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