在Python2.6中不赞成使用getslice，但在子类化元组时仍然使用它？

Question

Consider the following example, executed under Python 2.6.6 (which I'm unfortunately stuck with at the moment):

>>> class A:
...     def __getitem__(self, index):
...             print(type(index))
...     def __getslice__(self, start, end):
...             print("Don't call me, I'm deprecated")
...
>>> a = A()
>>> a[3]
<type 'int'>
>>> a[3:3]
<type 'slice'>

As it should be, the slicing also call __getitem__ . Now alter the definition to subclassing tuple :

>>> class B(tuple):
...     def __getitem__(self, index):
...             print(type(index))
...     def __getslice__(self, start, end):
...             print("Don't call me, I'm deprecated")
...
>>> b = B()
>>> b[3]
<type 'int'>
>>> b[3:]
Don't call me, I'm deprecated

Why is this happening?

Answer 1

Due to historical reasons, __getslice__ in some places still gets used for builtin types. So for a tuple, it does get used for the [i:j] style syntax of slicing. See: http://bugs.python.org/issue2041 for a brief description and the highlighted caveats in the getslice documentation