Add jaraco.classes-3.2.1

lib/jaraco/classes/properties.py

@@ -0,0 +1,171 @@
+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
+
+    '...' below should be 'jaraco.classes' but for pytest-dev/pytest#3396
+    >>> X.foo
+    <....properties.NonDataProperty object at ...>
+    """
+
+    def __init__(self, fget):
+        assert fget is not None, "fget cannot be none"
+        assert callable(fget), "fget must be callable"
+        self.fget = fget
+
+    def __get__(self, obj, objtype=None):
+        if obj is None:
+            return self
+        return self.fget(obj)
+
+
+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
+    """
+
+    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)
+
+    def __init__(self, fget, fset=None):
+        self.fget = self._fix_function(fget)
+        self.fset = fset
+        fset and self.setter(fset)
+
+    def __get__(self, instance, owner=None):
+        return self.fget.__get__(None, owner)()
+
+    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)
+
+    def setter(self, fset):
+        self.fset = self._fix_function(fset)
+        return self
+
+    @classmethod
+    def _fix_function(cls, fn):
+        """
+        Ensure fn is a classmethod or staticmethod.
+        """
+        if not isinstance(fn, (classmethod, staticmethod)):
+            return classmethod(fn)
+        return fn