__getslice__ changes integer arguments

[lorgandon]

BPO	1712236
Nosy	@rhettinger
Files	bug_example.txt: An example reproducing the bug.

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2007-05-18.23:51:44.000>
created_at = <Date 2007-05-03.18:20:45.000>
labels = ['interpreter-core']
title = '__getslice__ changes integer arguments'
updated_at = <Date 2007-05-18.23:51:44.000>
user = 'https://bugs.python.org/lorgandon'

bugs.python.org fields:

activity = <Date 2007-05-18.23:51:44.000>
actor = 'rhettinger'
assignee = 'none'
closed = True
closed_date = None
closer = None
components = ['Interpreter Core']
creation = <Date 2007-05-03.18:20:45.000>
creator = 'lorgandon'
dependencies = []
files = ['2367']
hgrepos = []
issue_num = 1712236
keywords = []
message_count = 3.0
messages = ['31941', '31942', '31943']
nosy_count = 2.0
nosy_names = ['rhettinger', 'lorgandon']
pr_nums = []
priority = 'normal'
resolution = 'wont fix'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue1712236'
versions = []

[lorgandon]

When using slicing for a sequence object, with a user defined __getslice__ function, the arguments to __getslice__ are changed.
This does not happen when __getslice__is called directly.
Attached is some code that demonstrates the problem.

I checked it on various versions, including my
"Python 2.5.1 (r251:54863, May 2 2007, 16:56:35)", on my Ubuntu machine.

Although __getslice__ is deprecated, there is still usage of the function, and a fix would be useful.

[lorgandon]

This also seems to be the cause of bug "[ 908441 ] default index for __getslice__ is not sys.maxint"

[rhettinger]

Unfortunately, this is a feature, not a bug. The relevant code is in Python/ceval.c apply_slice(). Calls to s[a:b] get pre-processed before being handed-off to s.__getslice__. This behavior has been around so long, that it is almost certain that there is a good body of existing code that relies on the behavior.