Pretty and useful exceptions in Python, automatically.

better-exceptions

Pretty and more helpful exceptions in Python, automatically.

Usage

Install better_exceptions via pip:

$ pip install better_exceptions

And set the BETTER_EXCEPTIONS environment variable to any value:

export BETTER_EXCEPTIONS=1  # Linux / OSX
setx BETTER_EXCEPTIONS 1    # Windows

That’s it!

Python REPL (Interactive Shell)

In order to use better_exceptions in the Python REPL, first install the package (as instructed above) and run:

$ python -m better_exceptions
Type "help", "copyright", "credits" or "license" for more information.
(BetterExceptionsConsole)
>>>

in order to drop into a better_exceptions-enabled Python interactive shell.

Advanced Usage

If you want to allow the entirety of values to be outputted instead of being truncated to a certain amount of characters:

import better_exceptions
better_exceptions.MAX_LENGTH = None

While using better_exceptions in production, do not forget to unset the BETTER_EXCEPTIONS variable to avoid leaking sensitive data in your logs.

Use with unittest

If you want to use better_exceptions to format unittest’s exception output, you can use the monkey patch below:

import sys
import unittest
import better_exceptions

def patch(self, err, test):
    lines = better_exceptions.format_exception(*err)
    if sys.version_info[0] == 2:
        return u"".join(lines).encode("utf-8")
    return "".join(lines)

unittest.result.TestResult._exc_info_to_string = patch

Note that this uses an undocumented method override, so it is not guaranteed to work on all platforms or versions of Python.

Django Usage

Tested with Django 1.11

Create a middleware exception handler in a file like myapp/middleware.py:

import sys
from better_exceptions import excepthook


class BetterExceptionsMiddleware(object):
    def __init__(self, get_response):
        self.get_response = get_response

    def __call__(self, request):
        return self.get_response(request)

    def process_exception(self, request, exception):
        excepthook(exception.__class__, exception, sys.exc_info()[2])
        return None

In settings.py, add your new class to the MIDDLEWARE list:

MIDDLEWARE = [
...
    'myapp.middleware.BetterExceptionsMiddleware',
]

example output:

Troubleshooting

If you do not see beautiful exceptions, first make sure that the environment variable does exist. You can try echo $BETTER_EXCEPTIONS (Linux / OSX) or echo %BETTER_EXCEPTIONS% (Windows). On Linux and OSX, the export command does not add the variable permanently, you will probably need to edit the ~/.profile file to make it persistent. On Windows, you need to open a new terminal after the setx command.

Check that there is no conflict with another library, and that the sys.excepthook function has been correctly replaced with the better_exceptions’s one. Sometimes other components can set up their own exception handlers, such as the python3-apport Ubuntu package that you may need to uninstall.

Make sure that you have not inadvertently deleted the better_exceptions_hook.pth file that should be in the same place as the better_exceptions folder where all of your Python packages are installed. Otherwise, try re-installing better_exceptions.

You can also try to manually activate the hook by adding import better_exceptions; better_exceptions.hook() at the beginning of your script.

Finally, if you still can not get this module to work, open a new issue by describing your problem precisely and detailing your configuration (Python and better_exceptions versions, OS, code snippet, interpeter, etc.) so that we can reproduce the bug you are experiencing.

License

Copyright © 2017, Josh Junon. Licensed under the MIT license.