def __iter__(self):
return iter(self.attributes)<EOL>
Iterate over the attributes.

        As ``Attributes`` is a dict-like object, iterating over it only returns keys.
        To iterate over values, ie ``Attribute`` instances, use for example ``.values()`` or
        ``.items()``.

        Returns
        -------
        iterator
            An iterator over the keys (ie classes) in the registry.

        Example
        -------

        >>> a = Attributes('foo', '_bar', Attribute(name="qux"))
        >>> for attr in sorted(a): print(attr)
        _bar
        foo
        qux
        >>> for attr in sorted(a.keys()): print(attr)
        _bar
        foo
        qux
        >>> from operator import attrgetter
        >>> for attr in sorted(a.values(), key=attrgetter('name')): print(attr)
        <Attribute '_bar'>
        <Attribute 'foo'>
        <Attribute 'qux'>
        >>> for name, attr in sorted(a.items()): print('%s : %s' % (name, attr))
        _bar : <Attribute '_bar'>
        foo : <Attribute 'foo'>
        qux : <Attribute 'qux'>