People have illusion that it is faster to visit the attribute defined by __slots__ . http://groups.google.com/group/comp.lang.python/msg/c4e413c3d86d80be
That is wrong. The following tests show it is slower. __slots__ are implemented at the class level by creating descriptors (Implementing Descriptors) for each variable name. It makes a little bit slower. So __slots__ just saves memory space by preventing creation of __dict__ and __weakref__ on each instance, while sacrifice performance and inheritance flexibility. http://groups.google.com/group/comp.lang.python/msg/6623e8b94b6d6934 D:\>d:\python-v3.1.2\python -mtimeit -s "class A(object): __slots__ = ('a', 'b', 'c')" -s "inst = A()" "inst.a=5; inst.b=6; inst.c=7" 1000000 loops, best of 3: 0.237 usec per loop D:\>d:\python-v3.1.2\python -mtimeit -s "class A(object): pass" -s "inst = A()" "inst.a=5 inst.b=6; inst.c=7" 1000000 loops, best of 3: 0.214 usec per loop D:\>d:\python-v2.6.4\python -mtimeit -s "class A(object): __slots__ = ('a', 'b', 'c')" -s "inst = A()" "inst.a=5; inst.b=6; inst.c=7" 1000000 loops, best of 3: 0.26 usec per loop D:\>d:\python-v2.6.4\python -mtimeit -s "class A(object): pass" -s "inst = A()" "inst.a=5; inst.b=6; inst.c=7" 1000000 loops, best of 3: 0.217 usec per loop -- http://mail.python.org/mailman/listinfo/python-list
