From eba46f3a8e60d5dca81c9a42d5e20408319ec768 Mon Sep 17 00:00:00 2001 From: Joshua Harlow Date: Mon, 29 Jun 2015 14:21:35 -0700 Subject: Provide a common exception caused by base class Both taskflow and tooz (and others of `raise_with_cause` should be able to use this as there base exception class to ensure that there usage of `raise_with_cause` works as expected). This adds the class that taskflow was/is using that provides a 'good enough' version exception chaining (and a decently useful `pformat` and `__str__` overrides that approximates the exception chaining message on py2.x). When used correctly this produces the following: http://paste.openstack.org/show/326021/ Which is a 'good enough' approximation of exception chaining on py2.x (and just uses the native exception chaining on py3.x) This also adds some basic tests to ensure the functionality provided continues to work as expected. Change-Id: If814816dec91f7da3c90f4b9b8e2d3cf7228b928 --- oslo_utils/excutils.py | 78 ++++++++++++++++++++++++++++++++++++++- oslo_utils/tests/test_excutils.py | 35 ++++++++++++++++++ 2 files changed, 112 insertions(+), 1 deletion(-) diff --git a/oslo_utils/excutils.py b/oslo_utils/excutils.py index a4eeace..dbaf0f6 100644 --- a/oslo_utils/excutils.py +++ b/oslo_utils/excutils.py @@ -18,6 +18,7 @@ Exception related utilities. """ import logging +import os import sys import time import traceback @@ -25,6 +26,80 @@ import traceback import six from oslo_utils._i18n import _LE +from oslo_utils import reflection + + +class CausedByException(Exception): + """Base class for exceptions which have associated causes. + + NOTE(harlowja): in later versions of python we can likely remove the need + to have a ``cause`` here as PY3+ have implemented :pep:`3134` which + handles chaining in a much more elegant manner. + + :param message: the exception message, typically some string that is + useful for consumers to view when debugging or analyzing + failures. + :param cause: the cause of the exception being raised, when provided this + should itself be an exception instance, this is useful for + creating a chain of exceptions for versions of python where + this is not yet implemented/supported natively. + """ + def __init__(self, message, cause=None): + super(CausedByException, self).__init__(message) + self.cause = cause + + def __bytes__(self): + return self.pformat().encode("utf8") + + def __str__(self): + return self.pformat() + + def _get_message(self): + # We must *not* call into the ``__str__`` method as that will + # reactivate the pformat method, which will end up badly (and doesn't + # look pretty at all); so be careful... + return self.args[0] + + def pformat(self, indent=2, indent_text=" ", show_root_class=False): + """Pretty formats a caused exception + any connected causes.""" + if indent < 0: + raise ValueError("Provided 'indent' must be greater than" + " or equal to zero instead of %s" % indent) + buf = six.StringIO() + if show_root_class: + buf.write(reflection.get_class_name(self, fully_qualified=False)) + buf.write(": ") + buf.write(self._get_message()) + active_indent = indent + next_up = self.cause + seen = [] + while next_up is not None and next_up not in seen: + seen.append(next_up) + buf.write(os.linesep) + if isinstance(next_up, CausedByException): + buf.write(indent_text * active_indent) + buf.write(reflection.get_class_name(next_up, + fully_qualified=False)) + buf.write(": ") + buf.write(next_up._get_message()) + else: + lines = traceback.format_exception_only(type(next_up), next_up) + for i, line in enumerate(lines): + buf.write(indent_text * active_indent) + if line.endswith("\n"): + # We'll add our own newlines on... + line = line[0:-1] + buf.write(line) + if i + 1 != len(lines): + buf.write(os.linesep) + if not isinstance(next_up, CausedByException): + # Don't go deeper into non-caused-by exceptions... as we + # don't know if there exception 'cause' attributes are even + # useable objects... + break + active_indent += indent + next_up = getattr(next_up, 'cause', None) + return buf.getvalue() def raise_with_cause(exc_cls, message, *args, **kwargs): @@ -40,7 +115,8 @@ def raise_with_cause(exc_cls, message, *args, **kwargs): inspected/retained on py2.x to get *similar* information as would be automatically included/obtainable in py3.x. - :param exc_cls: the exception class to raise. + :param exc_cls: the exception class to raise (typically one derived + from :py:class:`.CausedByException` or equivalent). :param message: the text/str message that will be passed to the exceptions constructor as its first positional argument. diff --git a/oslo_utils/tests/test_excutils.py b/oslo_utils/tests/test_excutils.py index c2626a4..60f752d 100644 --- a/oslo_utils/tests/test_excutils.py +++ b/oslo_utils/tests/test_excutils.py @@ -25,6 +25,41 @@ from oslo_utils import excutils mox = moxstubout.mox +class Fail1(excutils.CausedByException): + pass + + +class Fail2(excutils.CausedByException): + pass + + +class CausedByTest(test_base.BaseTestCase): + + def test_caused_by_explicit(self): + e = self.assertRaises(Fail1, + excutils.raise_with_cause, + Fail1, "I was broken", + cause=Fail2("I have been broken")) + self.assertIsInstance(e.cause, Fail2) + e_p = e.pformat() + self.assertIn("I have been broken", e_p) + self.assertIn("Fail2", e_p) + + def test_caused_by_implicit(self): + + def raises_chained(): + try: + raise Fail2("I have been broken") + except Fail2: + excutils.raise_with_cause(Fail1, "I was broken") + + e = self.assertRaises(Fail1, raises_chained) + self.assertIsInstance(e.cause, Fail2) + e_p = e.pformat() + self.assertIn("I have been broken", e_p) + self.assertIn("Fail2", e_p) + + class SaveAndReraiseTest(test_base.BaseTestCase): def test_save_and_reraise_exception(self): -- cgit v1.2.1