"""
A micro benchmark for attribute lookup in a class hierarcy.

Note: CPython contains an attribute lookup cache (look for
MCACHE in typeobject.c) which results into fast lookup in
the general case but defeats the purpose of this benchmark.

Therefore the benchmark is run a second time in a way that
circumvents the cache.
"""
import timeit

def make_classes(depth):
    assert depth > 0
    class root:
        def method(self): return 42

    current = root
    for r in range(depth):
        current = type("cls%d"%(r,), (current,), {})

    return current


class mystr (str):
    pass

def perform_benchmark(description, class_builder, name):
    cls1 = class_builder(1)
    cls10 = class_builder(10)
    cls100 = class_builder(100)

    assert getattr(cls1(), name)()
    assert getattr(cls10(), name)()
    assert getattr(cls100(), name)()

    print()
    print(description)
    t = timeit.Timer('getattr(obj, name)', setup='obj=cls1()', globals=locals())
    print("depth 1:   %.5s" % t.timeit() )

    t = timeit.Timer('getattr(obj, name)', setup='obj=cls10()', globals=locals())
    print("depth 10:  %.5s" % t.timeit() )

    t = timeit.Timer('getattr(obj, name)', setup='obj=cls100()', globals=locals())
    print("depth 100: %.5s" % t.timeit() )

    print()
    print(description + " using super")
    t = timeit.Timer('getattr(obj, name)', setup='obj=cls1(); obj=super(cls1, obj)', globals=locals())
    print("depth 1:   %.5s" % t.timeit() )

    t = timeit.Timer('getattr(obj, name)', setup='obj=cls10(); obj=super(cls10, obj)', globals=locals())
    print("depth 10:  %.5s" % t.timeit() )

    t = timeit.Timer('getattr(obj, name)', setup='obj=cls100(); obj=super(cls100, obj)', globals=locals())
    print("depth 100: %.5s" % t.timeit() )


perform_benchmark("Regular lookup", make_classes, "method")
perform_benchmark("Regular lookup without MCACHE", make_classes, mystr("method"))

if hasattr(type, '__getdescriptor__'):
    from _testcapi import TypeWithDefaultGetDescriptor

    class MetaClass (type):
        def __getdescriptor__(cls, name):
            try:
                return cls.__dict__[name]
            except KeyError:
                raise AttributeError(name)

    def make_classes_descr(depth):
        assert depth > 0
        class root (metaclass=MetaClass):
            def method(self): return 42

        current = root
        for r in range(depth):
            current = type("cls%d"%(r,), (current,), {})

        return current

    def make_classes_descr_C(depth):
        assert depth > 0
        class root (metaclass=TypeWithDefaultGetDescriptor):
            def method(self): return 42

        current = root
        for r in range(depth):
            current = type("cls%d"%(r,), (current,), {})

        return current

    perform_benchmark("__getdescriptor__ in C", make_classes_descr_C, "method")
    perform_benchmark("__getdescriptor__ in C without MCACHE", make_classes_descr_C, mystr("method"))

    perform_benchmark("__getdescriptor__ in Python", make_classes_descr, "method")
    perform_benchmark("__getdescriptor__ in Python without MCACHE", make_classes_descr, mystr("method"))