Method test_eval_order

Lib/test/test_decorators.py:233–292

(self)

                            "Application order of decorators is incorrect")

    def test_eval_order(self):
        # Evaluating a decorated function involves four steps for each
        # decorator-maker (the function that returns a decorator):
        #
        #    1: Evaluate the decorator-maker name
        #    2: Evaluate the decorator-maker arguments (if any)
        #    3: Call the decorator-maker to make a decorator
        #    4: Call the decorator
        #
        # When there are multiple decorators, these steps should be
        # performed in the above order for each decorator, but we should
        # iterate through the decorators in the reverse of the order they
        # appear in the source.

        actions = []

        def make_decorator(tag):
            actions.append('makedec' + tag)
            def decorate(func):
                actions.append('calldec' + tag)
                return func
            return decorate

        class NameLookupTracer (object):
            def __init__(self, index):
                self.index = index

            def __getattr__(self, fname):
                if fname == 'make_decorator':
                    opname, res = ('evalname', make_decorator)
                elif fname == 'arg':
                    opname, res = ('evalargs', str(self.index))
                else:
                    assert False, "Unknown attrname %s" % fname
                actions.append('%s%d' % (opname, self.index))
                return res

        c1, c2, c3 = map(NameLookupTracer, [ 1, 2, 3 ])

        expected_actions = [ 'evalname1', 'evalargs1', 'makedec1',
                             'evalname2', 'evalargs2', 'makedec2',
                             'evalname3', 'evalargs3', 'makedec3',
                             'calldec3', 'calldec2', 'calldec1' ]

        actions = []
        @c1.make_decorator(c1.arg)
        @c2.make_decorator(c2.arg)
        @c3.make_decorator(c3.arg)
        def foo(): return 42
        self.assertEqual(foo(), 42)

        self.assertEqual(actions, expected_actions)

        # Test the equivalence claim in chapter 7 of the reference manual.
        #
        actions = []
        def bar(): return 42
        bar = c1.make_decorator(c1.arg)(c2.make_decorator(c2.arg)(c3.make_decorator(c3.arg)(bar)))