gslib/lazy_wrapper.py

# -*- coding: utf-8 -*-
# Copyright 2018 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.
"""Provides a LazyWrapper class to defer loading a value until it's needed."""

from __future__ import absolute_import
from __future__ import print_function
from __future__ import division
from __future__ import unicode_literals


class LazyWrapper(object):
  """Wrapper for lazily instantiated objects."""

  def __init__(self, func):
    """The init method for LazyWrapper.

    Args:
      func: A function (lambda or otherwise) to lazily evaluate.
    """
    self._func = func

  def __int__(self):
    try:
      return int(self._value)
    except AttributeError:
      self._value = self._func()
      return int(self._value)

  def __eq__(self, other):
    try:
      return self._value == other
    except AttributeError:
      self._value = self._func()
      return self._value == other

  def __repr__(self):
    try:
      return str(self._value)
    except AttributeError:
      self._value = self._func()
      return str(self._value)

  def __str__(self):
    try:
      return str(self._value)
    except AttributeError:
      self._value = self._func()
      return str(self._value)

  def __call__(self):
    """The call method for a LazyWrapper object."""
    try:
      return self._value
    except AttributeError:
      self._value = self._func()
      return self._value

  def __len__(self):
    """The len method for a LazyWrapper object."""
    try:
      return len(self._value)
    except AttributeError:
      self.__call__()
      return len(self._value)

  def __iter__(self):
    """The iter method for a LazyWrapper object."""
    try:
      return self._value.__iter__()
    except AttributeError:
      self.__call__()
      return self._value.__iter__()