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+# Copyright 2015, 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
+
+
+class Outcome(object):
+ """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.
+ """
+ __metaclass__ = abc.ABCMeta
+
+ @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)