[Revised] 値をキャッシュするpropertyデコレータ

以前に書いたスニペットの書き直し. 一度読みだしたプロパティはオブジェクトが破棄されるまで保持し続けます. そういう仕様です.

デコレータ変数にキャッシュバックエンドを指定して, ちゃんとしたキャッシュを使う様にも書けるね
あとでやってみよう

dec.py

from functools import wraps
import mox
from unittest import TestCase

def cached_property(f):
    prefix = '_cached_property_'
    @wraps(f)
    def _cached_property(self):
        key = prefix + f.__name__
        if hasattr(self, key):
            return getattr(self, key)
        value = f(self)
        setattr(self, key, value)
        return value
    return property(_cached_property)


class TestCachedProperty(TestCase):
    def setUp(self):
        self.m = mox.Mox()

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

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

        # Procuder function that should be called twice.
        producer = self.m.CreateMockAnything()
        producer().AndReturn(30)
        producer().AndReturn(101)
        producer().AndReturn(None)
        producer().AndReturn(0)
        producer().AndReturn('')

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

        # Try
        self.m.ReplayAll()
        c = C()
        c2 = C()
        c3 = C()
        c4 = C()
        c5 = C()

        # Verify
        self.assertEqual(c.f, 30)
        self.assertEqual(c.f, 30)
        self.assertEqual(c._cached_property_f, 30)
        self.assertEqual(c2.f, 101)
        self.assertEqual(c2.f, 101)
        self.assertEqual(c2._cached_property_f, 101)
        self.assertEqual(c3.f, None)
        self.assertEqual(c3.f, None)
        self.assertEqual(c3._cached_property_f, None)
        self.assertEqual(c4.f, 0)
        self.assertEqual(c4.f, 0)
        self.assertEqual(c4._cached_property_f, 0)
        self.assertEqual(c5.f, '')
        self.assertEqual(c5.f, '')
        self.assertEqual(c5._cached_property_f, '')
        self.m.VerifyAll()

        return

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

        # Procuder function that should be called once.
        producer = self.m.CreateMockAnything()
        producer().AndReturn(30)
        producer().AndReturn(101)

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

        # Try
        self.m.ReplayAll()
        c = C()
        c2 = C()

        # Verify
        self.assertEqual(c.f, 30)
        self.assertEqual(c.f, 30)
        self.assertEqual(c._cached_property_f, 30)
        self.assertEqual(c2.f, 101)
        self.assertEqual(c2.f, 101)
        self.assertEqual(c2._cached_property_f, 101)
        self.m.VerifyAll()

        return