hasattr + __getattr__: I think this is Python bug

[Ian Kelly]

On Tue, Jul 20, 2010 at 9:39 AM, dmitrey <dmitrey.kroshko at scipy.org> wrote:
>>How about using a property instead of the __getattr__() hook? A property is a computed attribute that (among other things) plays much nicer with hasattr.
>
> Could anyone provide an example of it to be implemented, taking into
> account that a user can manually set "myObject.size" to an integer
> value?

The following will work in Python 2.6+:

class MyClass(object):

    @property
    def size(self):
        if not hasattr(self, '_size'):
            self._size = self._compute_size()
        return self._size

    @size.setter
    def size(self, value):
        self._size = value


To support earlier versions of Python, you would write it like so:

class MyClass(object):

    def _get_size(self):
        if not hasattr(self, '_size'):
            self._size = self._compute_size()
        return self._size

    def _set_size(self, value):
        self._size = value

    size = property(_get_size, _set_size)