85 lines
2.3 KiB
Python
85 lines
2.3 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2018 Google Inc. All Rights Reserved.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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"""Provides a LazyWrapper class to defer loading a value until it's needed."""
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from __future__ import absolute_import
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from __future__ import print_function
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from __future__ import division
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from __future__ import unicode_literals
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class LazyWrapper(object):
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"""Wrapper for lazily instantiated objects."""
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def __init__(self, func):
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"""The init method for LazyWrapper.
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Args:
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func: A function (lambda or otherwise) to lazily evaluate.
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"""
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self._func = func
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def __int__(self):
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try:
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return int(self._value)
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except AttributeError:
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self._value = self._func()
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return int(self._value)
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def __eq__(self, other):
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try:
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return self._value == other
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except AttributeError:
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self._value = self._func()
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return self._value == other
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def __repr__(self):
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try:
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return str(self._value)
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except AttributeError:
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self._value = self._func()
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return str(self._value)
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def __str__(self):
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try:
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return str(self._value)
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except AttributeError:
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self._value = self._func()
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return str(self._value)
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def __call__(self):
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"""The call method for a LazyWrapper object."""
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try:
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return self._value
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except AttributeError:
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self._value = self._func()
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return self._value
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def __len__(self):
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"""The len method for a LazyWrapper object."""
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try:
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return len(self._value)
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except AttributeError:
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self.__call__()
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return len(self._value)
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def __iter__(self):
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"""The iter method for a LazyWrapper object."""
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try:
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return self._value.__iter__()
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except AttributeError:
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self.__call__()
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return self._value.__iter__()
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