Is __getitem__ and __len__ implementations enough to make a user-defined class sliceable?

[santosowijaya]

BPO	21598

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assignee = None
closed_at = <Date 2014-05-29.02:29:08.413>
created_at = <Date 2014-05-29.02:18:10.673>
labels = ['invalid', 'type-bug', 'library']
title = 'Is __getitem__ and __len__ implementations enough to make a user-defined class sliceable?'
updated_at = <Date 2014-05-29.02:29:08.412>
user = 'https://bugs.python.org/santosowijaya'

bugs.python.org fields:

activity = <Date 2014-05-29.02:29:08.412>
actor = 'santoso.wijaya'
assignee = 'none'
closed = True
closed_date = <Date 2014-05-29.02:29:08.413>
closer = 'santoso.wijaya'
components = ['Library (Lib)']
creation = <Date 2014-05-29.02:18:10.673>
creator = 'santoso.wijaya'
dependencies = []
files = []
hgrepos = []
issue_num = 21598
keywords = []
message_count = 2.0
messages = ['219326', '219327']
nosy_count = 1.0
nosy_names = ['santoso.wijaya']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue21598'
versions = ['Python 2.7']

[santosowijaya]

The reference doc for Python data model says that __getslice__ is deprecated [1], and that __getitem__ should be used instead:

"""
Deprecated since version 2.0: Support slice objects as parameters to the __getitem__() method. (However, built-in types in CPython currently still implement __getslice__(). Therefore, you have to override it in derived classes when implementing slicing.)
"""

But I'm getting the following behavior when I try it myself. Is there something I'm missing?

$ python
Python 2.7.6 (default, Mar 22 2014, 22:59:56) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> class tup(object):
...     def __getitem__(self, i):
...             if i == 0: return 0
...             if i == 1: return 1
...             
KeyboardInterrupt
>>> class tup(object):
...     def __getitem__(self, i):
...             if i in (0, 1): return i
...             else: raise IndexError()
...     def __len__(self):
...             return 2
... 
>>> t = tup()
>>> len(t)
2
>>> t[0], t[1]
(0, 1)
>>> t[:2]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in __getitem__
IndexError
>>> t[:1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in __getitem__
IndexError

[1] https://docs.python.org/2/reference/datamodel.html#object.\_\_getslice__

[santosowijaya]

Hm. The docstring for __getitem__ doesn't mention it can/should be accepting slice object as argument. That's what I'm missing. Doc patch?