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#!/usr/bin/env python
# Copyright 2010 Google Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import cPickle
import os
import sys
class PersistentMixin:
"""Mixin class which provides facilities for persisting and restoring."""
@classmethod
def AssertWritable(cls, filename):
"""Raises an IOError if filename is not writable."""
persist_dir = os.path.dirname(os.path.abspath(filename))
if not os.path.exists(persist_dir):
raise IOError('Directory does not exist: %s' % persist_dir)
if os.path.exists(filename):
if not os.access(filename, os.W_OK):
raise IOError('Need write permission on file: %s' % filename)
elif not os.access(persist_dir, os.W_OK):
raise IOError('Need write permission on directory: %s' % persist_dir)
@classmethod
def Load(cls, filename):
"""Load an instance from filename."""
return cPickle.load(open(filename, 'rb'))
def Persist(self, filename):
"""Persist all state to filename."""
try:
original_checkinterval = sys.getcheckinterval()
sys.setcheckinterval(2**31-1) # Lock out other threads so nothing can
# modify |self| during pickling.
pickled_self = cPickle.dumps(self, cPickle.HIGHEST_PROTOCOL)
finally:
sys.setcheckinterval(original_checkinterval)
with open(filename, 'wb') as f:
f.write(pickled_self)
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