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Add copy of properties module from jaraco.classes 3.2.
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__all__ = ['properties'] | ||
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try: | ||
from jaraco.compat import properties # pragma: no-cover | ||
except ImportError: | ||
from . import _properties_compat as properties # pragma: no-cover |
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# from jaraco.classes 3.2.2 | ||
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class NonDataProperty: | ||
"""Much like the property builtin, but only implements __get__, | ||
making it a non-data property, and can be subsequently reset. | ||
See http://users.rcn.com/python/download/Descriptor.htm for more | ||
information. | ||
>>> class X(object): | ||
... @NonDataProperty | ||
... def foo(self): | ||
... return 3 | ||
>>> x = X() | ||
>>> x.foo | ||
3 | ||
>>> x.foo = 4 | ||
>>> x.foo | ||
4 | ||
""" | ||
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def __init__(self, fget): | ||
assert fget is not None, "fget cannot be none" | ||
assert callable(fget), "fget must be callable" | ||
self.fget = fget | ||
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def __get__(self, obj, objtype=None): | ||
if obj is None: | ||
return self | ||
return self.fget(obj) | ||
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class classproperty: | ||
""" | ||
Like @property but applies at the class level. | ||
>>> class X(metaclass=classproperty.Meta): | ||
... val = None | ||
... @classproperty | ||
... def foo(cls): | ||
... return cls.val | ||
... @foo.setter | ||
... def foo(cls, val): | ||
... cls.val = val | ||
>>> X.foo | ||
>>> X.foo = 3 | ||
>>> X.foo | ||
3 | ||
>>> x = X() | ||
>>> x.foo | ||
3 | ||
>>> X.foo = 4 | ||
>>> x.foo | ||
4 | ||
Setting the property on an instance affects the class. | ||
>>> x.foo = 5 | ||
>>> x.foo | ||
5 | ||
>>> X.foo | ||
5 | ||
>>> vars(x) | ||
{} | ||
>>> X().foo | ||
5 | ||
Attempting to set an attribute where no setter was defined | ||
results in an AttributeError: | ||
>>> class GetOnly(metaclass=classproperty.Meta): | ||
... @classproperty | ||
... def foo(cls): | ||
... return 'bar' | ||
>>> GetOnly.foo = 3 | ||
Traceback (most recent call last): | ||
... | ||
AttributeError: can't set attribute | ||
It is also possible to wrap a classmethod or staticmethod in | ||
a classproperty. | ||
>>> class Static(metaclass=classproperty.Meta): | ||
... @classproperty | ||
... @classmethod | ||
... def foo(cls): | ||
... return 'foo' | ||
... @classproperty | ||
... @staticmethod | ||
... def bar(): | ||
... return 'bar' | ||
>>> Static.foo | ||
'foo' | ||
>>> Static.bar | ||
'bar' | ||
*Legacy* | ||
For compatibility, if the metaclass isn't specified, the | ||
legacy behavior will be invoked. | ||
>>> class X: | ||
... val = None | ||
... @classproperty | ||
... def foo(cls): | ||
... return cls.val | ||
... @foo.setter | ||
... def foo(cls, val): | ||
... cls.val = val | ||
>>> X.foo | ||
>>> X.foo = 3 | ||
>>> X.foo | ||
3 | ||
>>> x = X() | ||
>>> x.foo | ||
3 | ||
>>> X.foo = 4 | ||
>>> x.foo | ||
4 | ||
Note, because the metaclass was not specified, setting | ||
a value on an instance does not have the intended effect. | ||
>>> x.foo = 5 | ||
>>> x.foo | ||
5 | ||
>>> X.foo # should be 5 | ||
4 | ||
>>> vars(x) # should be empty | ||
{'foo': 5} | ||
>>> X().foo # should be 5 | ||
4 | ||
""" | ||
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class Meta(type): | ||
def __setattr__(self, key, value): | ||
obj = self.__dict__.get(key, None) | ||
if type(obj) is classproperty: | ||
return obj.__set__(self, value) | ||
return super().__setattr__(key, value) | ||
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def __init__(self, fget, fset=None): | ||
self.fget = self._ensure_method(fget) | ||
self.fset = fset | ||
fset and self.setter(fset) | ||
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def __get__(self, instance, owner=None): | ||
return self.fget.__get__(None, owner)() | ||
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def __set__(self, owner, value): | ||
if not self.fset: | ||
raise AttributeError("can't set attribute") | ||
if type(owner) is not classproperty.Meta: | ||
owner = type(owner) | ||
return self.fset.__get__(None, owner)(value) | ||
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def setter(self, fset): | ||
self.fset = self._ensure_method(fset) | ||
return self | ||
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@classmethod | ||
def _ensure_method(cls, fn): | ||
""" | ||
Ensure fn is a classmethod or staticmethod. | ||
""" | ||
needs_method = not isinstance(fn, (classmethod, staticmethod)) | ||
return classmethod(fn) if needs_method else fn |
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