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133 lines
3.8 KiB
Python
133 lines
3.8 KiB
Python
#!/usr/bin/env python
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#
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# A library that provides a Python interface to the Telegram Bot API
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# Copyright (C) 2015-2021
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# Leandro Toledo de Souza <devs@python-telegram-bot.org>
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU Lesser Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU Lesser Public License for more details.
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#
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# You should have received a copy of the GNU Lesser Public License
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# along with this program. If not, see [http://www.gnu.org/licenses/].
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"""This module contains the DefaultValue class.
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.. versionchanged:: 14.0
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Previously, the contents of this module were available through the (no longer existing)
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module ``telegram.utils.helpers``.
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Warning:
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Contents of this module are intended to be used internally by the library and *not* by the
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user. Changes to this module are not considered breaking changes and may not be documented in
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the changelog.
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"""
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from typing import Generic, overload, Union, TypeVar
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DVType = TypeVar('DVType', bound=object)
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OT = TypeVar('OT', bound=object)
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class DefaultValue(Generic[DVType]):
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"""Wrapper for immutable default arguments that allows to check, if the default value was set
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explicitly. Usage::
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default_one = DefaultValue(1)
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def f(arg=default_one):
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if arg is default_one:
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print('`arg` is the default')
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arg = arg.value
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else:
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print('`arg` was set explicitly')
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print(f'`arg` = {str(arg)}')
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This yields::
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>>> f()
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`arg` is the default
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`arg` = 1
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>>> f(1)
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`arg` was set explicitly
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`arg` = 1
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>>> f(2)
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`arg` was set explicitly
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`arg` = 2
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Also allows to evaluate truthiness::
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default = DefaultValue(value)
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if default:
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...
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is equivalent to::
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default = DefaultValue(value)
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if value:
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...
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``repr(DefaultValue(value))`` returns ``repr(value)`` and ``str(DefaultValue(value))`` returns
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``f'DefaultValue({value})'``.
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Args:
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value (:obj:`obj`): The value of the default argument
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Attributes:
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value (:obj:`obj`): The value of the default argument
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"""
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__slots__ = ('value',)
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def __init__(self, value: DVType = None):
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self.value = value
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def __bool__(self) -> bool:
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return bool(self.value)
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@overload
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@staticmethod
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def get_value(obj: 'DefaultValue[OT]') -> OT:
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...
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@overload
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@staticmethod
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def get_value(obj: OT) -> OT:
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...
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@staticmethod
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def get_value(obj: Union[OT, 'DefaultValue[OT]']) -> OT:
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"""
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Shortcut for::
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return obj.value if isinstance(obj, DefaultValue) else obj
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Args:
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obj (:obj:`object`): The object to process
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Returns:
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Same type as input, or the value of the input: The value
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"""
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return obj.value if isinstance(obj, DefaultValue) else obj # type: ignore[return-value]
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# This is mostly here for readability during debugging
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def __str__(self) -> str:
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return f'DefaultValue({self.value})'
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# This is here to have the default instances nicely rendered in the docs
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def __repr__(self) -> str:
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return repr(self.value)
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DEFAULT_NONE: DefaultValue = DefaultValue(None)
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""":class:`DefaultValue`: Default :obj:`None`"""
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DEFAULT_FALSE: DefaultValue = DefaultValue(False)
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""":class:`DefaultValue`: Default :obj:`False`"""
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DEFAULT_20: DefaultValue = DefaultValue(20)
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""":class:`DefaultValue`: Default :obj:`20`"""
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