Implement lazy evaluation in Python.
>>> from lazy import LazyBase
>>> class LazyInteger(LazyBase):
... _type = int
... _operators = ('__add__', '__mul__')
...
>>> two = LazyInteger.lazify(2)
>>> three = LazyInteger.lazify(3)
>>> five = two + three
>>> five.value
5
>>> six = two * three
>>> six.value
6