A simple cache of values in the property decorator. Read only. Note that it keeps caching until the object is deleted.

def cached_ro_property(f):
    cache = [None]
    def _cached_ro_property(*args, **kargs):
        if cache[0]:
            return cache[0]
        cache[0] = f(*args, **kargs)
        return cache[0]
    return property(_cached_ro_property)


from django.test import TestCase
import mox


class TestCachedRoProperty(TestCase):
    """Test for cached_ro_property decorator."""
    
    def setUp(self):
        self.m = mox.Mox()

    def tearDown(self):
        self.m.UnsetStubs()
        self.m = None

    def test_call_1(self):
        """Simple call."""

        from decorators import cached_ro_property

        # Procuder function that should be called once.
        producer = self.m.CreateMockAnything()
        producer().AndReturn(30)

        class C(object):
            @cached_ro_property
            def f(self):
                return producer()

        self.m.ReplayAll()
        c = C()

        self.assertEqual(c.f, 30)
        self.assertEqual(c.f, 30)
        self.m.VerifyAll()

    def test_call_2(self):
        """Check that property function reference self."""

        from decorators import cached_ro_property

        # Procuder function that should be called once.
        producer = self.m.CreateMockAnything()
        producer().AndReturn(30)

        class C(object):
            @cached_ro_property
            def f(self):
                return self.g()
            def g(self):
                return producer()

        self.m.ReplayAll()
        c = C()

        self.assertEqual(c.f, 30)
        self.assertEqual(c.f, 30)
        self.m.VerifyAll()