reflected greater than magic methods

__lt__ is __gt__'s counterpart; you'll need to implement __lt__. While you're at it, you should probably implement __le__ and __ge__.

You can use a functools.total_ordering decorator to create the missing comparison methods for you:

import functools

@functools.total_ordering
class Property():
    ...

Then you get False, False, False. Do make sure to read its documentation, though.

Since you've declared the __float__() method, you could always write it as:

print float(y) > float(x)