# Copyright 2008-2015 Nokia Networks
# Copyright 2016- Robot Framework Foundation
#
# 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.
import sys
from typing import Callable, Generic, overload, TypeVar, Type, Union
T = TypeVar('T')
V = TypeVar('V')
A = TypeVar('A')
class setter(Generic[T, V, A]):
"""Modify instance attributes only when they are set, not when they are get.
Usage::
@setter
def source(self, source: str|Path) -> Path:
return source if isinstance(source, Path) else Path(source)
The setter method is called when the attribute is assigned like::
instance.source = 'example.txt'
and the returned value is stored in the instance in an attribute like
``_setter__source``. When the attribute is accessed, the stored value is
returned.
The above example is equivalent to using the standard ``property`` as
follows. The main benefit of using ``setter`` is that it avoids a dummy
getter method::
@property
def source(self) -> Path:
return self._source
@source.setter
def source(self, source: src|Path):
self._source = source if isinstance(source, Path) else Path(source)
When using ``setter`` with ``__slots__``, the special ``_setter__xxx``
attributes needs to be added to ``__slots__`` as well. The provided
:class:`SetterAwareType` metaclass can take care of that automatically.
"""
def __init__(self, method: Callable[[T, V], A]):
self.method = method
self.attr_name = '_setter__' + method.__name__
self.__doc__ = method.__doc__
@overload
def __get__(self, instance: None, owner: Type[T]) -> 'setter':
...
@overload
def __get__(self, instance: T, owner: Type[T]) -> A:
...
def __get__(self, instance: Union[T, None], owner: Type[T]) -> Union[A, 'setter']:
if instance is None:
return self
try:
return getattr(instance, self.attr_name)
except AttributeError:
raise AttributeError(self.method.__name__)
def __set__(self, instance: T, value: V):
if instance is not None:
setattr(instance, self.attr_name, self.method(instance, value))
class SetterAwareType(type):
"""Metaclass for adding attributes used by :class:`setter` to ``__slots__``."""
def __new__(cls, name, bases, dct):
if '__slots__' in dct:
slots = list(dct['__slots__'])
for item in dct.values():
if isinstance(item, setter):
slots.append(item.attr_name)
dct['__slots__'] = slots
return type.__new__(cls, name, bases, dct)
if sys.version_info < (3, 7):
def __getitem__(self, item):
return self