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#!/usr/bin/python
#
# Copyright 2012 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.
"""Functionality to allow easily retrieving certain filter objects."""
__author__ = 'msu@google.com (Martin Suess)'
import definition_filter
import file_filter
DEFINITION_FILTER = 1
FILE_FILTER = 2
GLOBAL_FILTER = 3
PRE_FILTERS = 'PreFilters'
POST_FILTERS = 'PostFilters'
class Error(Exception):
"""Base error class."""
class FilterIdentificationError(Error):
"""Exception to use when FilterFactory fails to identify the Filter."""
class FilterFactory(object):
"""Functionality to get a filter object easily based on its name.
This class can be initialized and the GetFilter() method allows retrieving a
specific filter based on the name of the filter and the scope (global, file
and definition).
"""
def __init__(self):
"""Initializer."""
self._filters = {
DEFINITION_FILTER: {
'PostFilters': {
'SortFilter': definition_filter.SortFilter,
'AlignFilter': definition_filter.AlignFilter,
},
},
FILE_FILTER: {
'PostFilters': {
'PrintFilter': file_filter.PrintFilter,
'WriteFileFilter': file_filter.WriteFileFilter,
},
},
GLOBAL_FILTER: {
'PreFilters': {
},
'PostFilters': {
},
},
}
def GetFilter(self, scope, identifier, sequence):
"""Returns a specific filter instance based on the identifier.
Args:
scope: Type of filter to be returned. Valid types are listed as globals
in the beginning of this module.
identifier: String identifier for the filter to get.
sequence: String identifier for the sequence information to determine
when the filter should be applied. Valid values:
- 'PreFilters': Filters that are applied before processing the data
(e.g. before the definition is created).
- 'PostFilters': Filters that are applied after processing the data
(e.g. after the definition has been created).
Raises:
FilterIdentificationError: If the filter cannot be identified.
Returns:
Filter instance based on the identifier passed in.
"""
if scope not in self._filters:
raise FilterIdentificationError(
'Filter scope \'%d\' could not be found in filters.' % scope)
if sequence not in self._filters[scope]:
raise FilterIdentificationError(
'Filter sequence \'%s\' is not applicable to scope \'%d\'.' % (
sequence, scope))
filters = self._filters[scope][sequence]
if identifier not in filters:
raise FilterIdentificationError(
'Filter \'%s\' could not be identified. Wrong scope (%d) or sequence'
' (%s)?' % (identifier, scope, sequence))
return filters[identifier]()
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