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defaultvalue.py
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defaultvalue.py
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#!/usr/bin/env python
#
# A library that provides a Python interface to the Telegram Bot API
# Copyright (C) 2015-2023
# Leandro Toledo de Souza <devs@python-telegram-bot.org>
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser Public License for more details.
#
# You should have received a copy of the GNU Lesser Public License
# along with this program. If not, see [http://www.gnu.org/licenses/].
"""This module contains the DefaultValue class.
.. versionchanged:: 20.0
Previously, the contents of this module were available through the (no longer existing)
module ``telegram._utils.helpers``.
Warning:
Contents of this module are intended to be used internally by the library and *not* by the
user. Changes to this module are not considered breaking changes and may not be documented in
the changelog.
"""
from typing import Generic, TypeVar, Union, overload
DVType = TypeVar("DVType", bound=object) # pylint: disable=invalid-name
OT = TypeVar("OT", bound=object)
class DefaultValue(Generic[DVType]):
"""Wrapper for immutable default arguments that allows to check, if the default value was set
explicitly. Usage::
default_one = DefaultValue(1)
def f(arg=default_one):
if arg is default_one:
print('`arg` is the default')
arg = arg.value
else:
print('`arg` was set explicitly')
print(f'`arg` = {str(arg)}')
This yields::
>>> f()
`arg` is the default
`arg` = 1
>>> f(1)
`arg` was set explicitly
`arg` = 1
>>> f(2)
`arg` was set explicitly
`arg` = 2
Also allows to evaluate truthiness::
default = DefaultValue(value)
if default:
...
is equivalent to::
default = DefaultValue(value)
if value:
...
``repr(DefaultValue(value))`` returns ``repr(value)`` and ``str(DefaultValue(value))`` returns
``f'DefaultValue({value})'``.
Args:
value (:class:`object`): The value of the default argument
Attributes:
value (:class:`object`): The value of the default argument
"""
__slots__ = ("value",)
def __init__(self, value: DVType):
self.value: DVType = value
def __bool__(self) -> bool:
return bool(self.value)
# This is mostly here for readability during debugging
def __str__(self) -> str:
return f"DefaultValue({self.value})"
# This is here to have the default instances nicely rendered in the docs
def __repr__(self) -> str:
return repr(self.value)
@overload
@staticmethod
def get_value(obj: "DefaultValue[OT]") -> OT:
...
@overload
@staticmethod
def get_value(obj: OT) -> OT:
...
@staticmethod
def get_value(obj: Union[OT, "DefaultValue[OT]"]) -> OT:
"""Shortcut for::
return obj.value if isinstance(obj, DefaultValue) else obj
Args:
obj (:obj:`object`): The object to process
Returns:
Same type as input, or the value of the input: The value
"""
return obj.value if isinstance(obj, DefaultValue) else obj
DEFAULT_NONE: DefaultValue[None] = DefaultValue(None)
""":class:`DefaultValue`: Default :obj:`None`"""
DEFAULT_FALSE: DefaultValue[bool] = DefaultValue(False)
""":class:`DefaultValue`: Default :obj:`False`"""
DEFAULT_TRUE: DefaultValue[bool] = DefaultValue(True)
""":class:`DefaultValue`: Default :obj:`True`
.. versionadded:: 20.0
"""