Source code for budou.cachefactory
# Copyright 2017 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.
"""Budou cache factory class."""
from abc import ABCMeta, abstractmethod
import os
import pickle
import six
[docs]def load_cache(filename=None):
"""Returns a cache service.
If Google App Engine Standard Environment's memcache is available, this uses
memcache as the backend. Otherwise, this uses :obj:`pickle` to cache
the outputs in the local file system.
Args:
filename (str, optional): The file path to the cache file. This is
used only when :obj:`pickle` is used as the backend.
Returns:
A cache system (:obj:`budou.cachefactory.BudouCache`)
"""
try:
return AppEngineMemcache()
except ImportError:
return PickleCache(filename)
[docs]@six.add_metaclass(ABCMeta)
class BudouCache:
"""Base class for cache system.
"""
[docs] @abstractmethod
def get(self, key):
"""Abstract method: Gets a value by a key.
Args:
key (str): Key to retrieve the value.
Returns:
Retrieved value (str or None).
Raises:
NotImplementedError: If it's not implemented.
"""
raise NotImplementedError()
[docs] @abstractmethod
def set(self, key, val):
"""Abstract method: Sets a value in a key.
Args:
key (str): Key for the value.
val (str): Value to set.
Raises:
NotImplementedError: If it's not implemented.
"""
raise NotImplementedError()
[docs]class PickleCache(BudouCache):
"""Cache system with :obj:`pickle` backend.
Args:
filename (str): The file path to the cache file.
Attributes:
filename (str): The file path to the cache file.
"""
DEFAULT_FILE_NAME = '/tmp/budou-cache.pickle'
""" The default path to the cache file.
"""
def __init__(self, filename):
self.filename = filename if filename else self.DEFAULT_FILE_NAME
[docs] def get(self, key):
"""Gets a value by a key.
Args:
key (str): Key to retrieve the value.
Returns: Retrieved value (str or None).
"""
self._create_file_if_none_exists()
with open(self.filename, 'rb') as file_object:
cache_pickle = pickle.load(file_object)
val = cache_pickle.get(key, None)
return val
[docs] def set(self, key, val):
"""Sets a value in a key.
Args:
key (str): Key for the value.
val (str): Value to set.
"""
self._create_file_if_none_exists()
with open(self.filename, 'r+b') as file_object:
cache_pickle = pickle.load(file_object)
cache_pickle[key] = val
file_object.seek(0)
pickle.dump(cache_pickle, file_object)
def _create_file_if_none_exists(self):
if os.path.exists(self.filename):
return
with open(self.filename, 'wb') as file_object:
pickle.dump({}, file_object)
[docs]class AppEngineMemcache(BudouCache):
"""Cache system with :obj:`google.appengine.api.memcache` backend.
Attributes:
memcache (:obj:`google.appengine.api.memcache`): Memcache service.
"""
def __init__(self):
from google.appengine.api import memcache
self.memcache = memcache
[docs] def get(self, key):
"""Gets a value by a key.
Args:
key (str): Key to retrieve the value.
Returns:
Retrieved value (str or None).
"""
return self.memcache.get(key, None)
[docs] def set(self, key, val):
"""Sets a value in a key.
Args:
key (str): Key for the value.
val (str): Value to set.
"""
self.memcache.set(key, val)