Errors and Exceptions

Exceptions and Tracebacks

If you are using actions you don’t need to do anything special to log exceptions: if an exception is thrown within the context of an action and not caught, the action will be marked as failed and the exception will be logged with it.

If you get a completely unexpected exception you may wish to log a traceback to aid debugging:

from eliot import write_traceback

class YourClass(object):

    def run(self):

Custom Exception Logging

By default both failed actions and tracebacks log the class and string-representation of the logged exception. You can add additional fields to these messages by registering a callable that converts exceptions into fields. If no extraction function is registered for a class Eliot will look for registered functions for the exception’s base classes.

For example, the following registration means all failed actions that fail with a MyException will have a code field in the action end message, as will tracebacks logged with this exception:

class MyException(Exception):
    def __init__(self, code):
        self.code = code

from eliot import register_exception_extractor
register_exception_extractor(MyException, lambda e: {"code": e.code})

By default Eliot will automatically extract fields from OSError, IOError and other subclasses of Python’s EnvironmentError.