This is a backport of the BaseExceptionGroup and ExceptionGroup classes from Python 3.11.

It contains the following:

  • The exceptiongroup.BaseExceptionGroup and exceptiongroup.ExceptionGroup classes
  • A utility function (exceptiongroup.catch()) for catching exceptions possibly nested in an exception group
  • Patches to the TracebackException class that properly formats exception groups (installed on import)
  • An exception hook that handles formatting of exception groups through TracebackException (installed on import)

The only difference with the Python 3.11 standard library implementation is that there is no __note__ attribute in BaseExceptionGroup or ExceptionGroup.

If this package is imported on Python 3.11 or later, the built-in implementations of the exception group classes are used instead, TracebackException is not monkey patched and the exception hook won't be installed.

.. seealso:: https://docs.python.org/3/library/exceptions.html

Catching exceptions

Due to the lack of the except* syntax introduced by PEP 654 in earlier Python versions, you need to use exceptiongroup.catch() to catch exceptions that are potentially nested inside an exception group. This function returns a context manager that calls the given handler for any exceptions matching the first argument.

So, the following Python 3.11+ code:

try:
    ...
except* (ValueError, KeyError) as exc:
    print('Caught exception:', type(exc))

would be written as follows:

from exceptiongroup import catch

def handler(exc: Exception) -> None:
    print('Caught exception:', type(exc))

with catch((ValueError, KeyError), handler):
    ...

Note

Just like with except*, you cannot handle BaseExceptionGroup or ExceptionGroup with catch().

GitHub - agronholm/exceptiongroup at pythonawesome.com
Backport of PEP 654 (exception groups). Contribute to agronholm/exceptiongroup development by creating an account on GitHub.
GitHubagronholm