test.py

import time                                                

def lazy(attr_name):

    def lazy_wrapper(fn):
        name = attr_name

        def _lazyprop(self):

            if not hasattr(self, name):
                setattr(self, name, fn(self))

            return getattr(self, name)

        return _lazyprop

    return lazy_wrapper

def timeit(method):

    def timed(*args, **kw):
        ts = time.time()
        result = method(*args, **kw)
        te = time.time()

        print '%r (%r, %r) %2.2f sec' % \
              (method.__name__, args, kw, te-ts)
        return result

    return timed

class Foo(object):

    @property
    @lazy('_foo')
    def bar(self):
        return []

class Bar(object):
    @property
    def foo(self):
        if not hasattr(self, '_foo'):
            self._foo = []

        return self._foo

@timeit
def f1():
    time.sleep(1)
    for i in range(1000000):
        Foo().bar
    print 'f1'

@timeit
def f2():
    time.sleep(2)
    for i in range(1000000):
        Bar().foo
    print 'f2'

f1()
f2()