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# Copyright 2015-2016, Google Inc.
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are
# met:
#
# * Redistributions of source code must retain the above copyright
# notice, this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above
# copyright notice, this list of conditions and the following disclaimer
# in the documentation and/or other materials provided with the
# distribution.
# * Neither the name of Google Inc. nor the names of its
# contributors may be used to endorse or promote products derived from
# this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
"""Utilities for working with callables."""
import abc
import collections
import enum
import functools
import logging
import six
class Outcome(six.with_metaclass(abc.ABCMeta)):
"""A sum type describing the outcome of some call.
Attributes:
kind: One of Kind.RETURNED or Kind.RAISED respectively indicating that the
call returned a value or raised an exception.
return_value: The value returned by the call. Must be present if kind is
Kind.RETURNED.
exception: The exception raised by the call. Must be present if kind is
Kind.RAISED.
"""
@enum.unique
class Kind(enum.Enum):
"""Identifies the general kind of the outcome of some call."""
RETURNED = object()
RAISED = object()
class _EasyOutcome(
collections.namedtuple(
'_EasyOutcome', ['kind', 'return_value', 'exception']),
Outcome):
"""A trivial implementation of Outcome."""
def _call_logging_exceptions(behavior, message, *args, **kwargs):
try:
return _EasyOutcome(Outcome.Kind.RETURNED, behavior(*args, **kwargs), None)
except Exception as e: # pylint: disable=broad-except
logging.exception(message)
return _EasyOutcome(Outcome.Kind.RAISED, None, e)
def with_exceptions_logged(behavior, message):
"""Wraps a callable in a try-except that logs any exceptions it raises.
Args:
behavior: Any callable.
message: A string to log if the behavior raises an exception.
Returns:
A callable that when executed invokes the given behavior. The returned
callable takes the same arguments as the given behavior but returns a
future.Outcome describing whether the given behavior returned a value or
raised an exception.
"""
@functools.wraps(behavior)
def wrapped_behavior(*args, **kwargs):
return _call_logging_exceptions(behavior, message, *args, **kwargs)
return wrapped_behavior
def call_logging_exceptions(behavior, message, *args, **kwargs):
"""Calls a behavior in a try-except that logs any exceptions it raises.
Args:
behavior: Any callable.
message: A string to log if the behavior raises an exception.
*args: Positional arguments to pass to the given behavior.
**kwargs: Keyword arguments to pass to the given behavior.
Returns:
An Outcome describing whether the given behavior returned a value or raised
an exception.
"""
return _call_logging_exceptions(behavior, message, *args, **kwargs)
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