from collections import abc


class ClassProperty(property):
    """
    An implementation of a property callable on a class. Used to decorate a
    classmethod but to then treat it like a property.

    Example:

    >>> class MyClass:
    ...    @ClassProperty
    ...    @classmethod
    ...    def skillz(cls):
    ...        return cls.__name__.startswith('My')
    >>> MyClass.skillz
    True
    >>> class YourClass(MyClass): pass
    >>> YourClass.skillz
    False
    """

    def __get__(self, cls, owner):
        return self.fget.__get__(None, owner)()


# borrowed from jaraco.util.dictlib


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:
    ...   @NonDataProperty
    ...   def foo(self):
    ...     return 3
    >>> x = X()
    >>> x.foo
    3
    >>> x.foo = 4
    >>> x.foo
    4
    """

    def __init__(self, fget):
        assert fget is not None, "fget cannot be none"
        assert isinstance(fget, abc.Callable), "fget must be callable"
        self.fget = fget

    def __get__(self, obj, objtype=None):
        if obj is None:
            return self
        return self.fget(obj)
