[issue13340] list.index does not accept None as start or stop

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Thank you for the reminder Irit. Your comments for issues and PRs are really 
helpful. Thank you for all this!

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resolution:  -> out of date
stage: needs patch -> resolved
status: open -> closed

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[issue13340] list.index does not accept None as start or stop

[Irit Katriel]

Irit Katriel  added the comment:

The error message was fixed under issue29935, so I think this issue can now be 
closed.

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[issue13340] list.index does not accept None as start or stop

[Berker Peksag]

Berker Peksag added the comment:

See http://thread.gmane.org/gmane.comp.python.devel/127502 for the python-dev 
thread.

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versions: +Python 3.6 -Python 3.4

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[issue13340] list.index does not accept None as start or stop

[R. David Murray]

R. David Murray added the comment:

Per discussion in the issue, I'm changing this to a bugfix on the message text. 
 If the python-dev discussion resulted (or results in the future) in a desire 
to change the API, that should be a new issue.

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stage: commit review -> needs patch
versions: +Python 2.7, Python 3.4, Python 3.5 -Python 3.3

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[issue13340] list.index does not accept None as start or stop

[Aaron Meurer]

Changes by Aaron Meurer :


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[issue13340] list.index does not accept None as start or stop

[Éric Araujo]

Changes by Éric Araujo :


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priority: high -> normal
stage: committed/rejected -> commit review
versions:  -Python 2.7, Python 3.2

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[issue13340] list.index does not accept None as start or stop

[Petri Lehtinen]

Petri Lehtinen  added the comment:

It's now reverted on all branches. I posted to python-dev alreay earlier.

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[issue13340] list.index does not accept None as start or stop

[Roundup Robot]

Roundup Robot  added the comment:

New changeset 19ffa12ffdd4 by Petri Lehtinen in branch '2.7':
Revert "Accept None as start and stop parameters for list.index() and 
tuple.index()"
http://hg.python.org/cpython/rev/19ffa12ffdd4

New changeset ed0e85efac47 by Petri Lehtinen in branch '3.2':
Revert "Accept None as start and stop parameters for list.index() and 
tuple.index()"
http://hg.python.org/cpython/rev/ed0e85efac47

New changeset 106f9e1ad7ab by Petri Lehtinen in branch 'default':
Revert "Accept None as start and stop parameters for list.index() and 
tuple.index()"
http://hg.python.org/cpython/rev/106f9e1ad7ab

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[issue13340] list.index does not accept None as start or stop

[Raymond Hettinger]

Raymond Hettinger  added the comment:

One other thought:  the API for list.index() doesn't exist in isolation.  There 
is also str.index, the sequence abstract base class, and tons of code that has 
been written to emulate lists.  This is an ancient API (approx 20 years) and 
should only be changed with care.

IOW, I don't think this change should have been made at all, at least not 
without a discussion on python-dev and motivating use cases.

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resolution: fixed -> 

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[issue13340] list.index does not accept None as start or stop

[Raymond Hettinger]

Raymond Hettinger  added the comment:

> There's still the question whether {list,tuple}.index() should accept None or 
> not.

The API should not be changed for Py2.7 and Py3.2.  Those changesets should be 
reverted.

For Py3.3, it is open to discussion, but we probably don't need the change 
(making every other implementation also change for nearly zero benefit).

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[issue13340] list.index does not accept None as start or stop

[Petri Lehtinen]

Petri Lehtinen  added the comment:

> Or am I misunderstanding?

Ah, no, sorry. I wasn't aware of this.

Now the error message set by _PyEval_SliceIndex() makes sense. It doesn't 
itself accept None, but apply_slice() and assign_slice() handle the None case.

There's still the question whether {list,tuple}.index() should accept None or 
not.

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[issue13340] list.index does not accept None as start or stop

[Mark Dickinson]

Mark Dickinson  added the comment:

> What do you suggest? Doing it in _PyEval_SliceIndex() in 2.7 is
> problematic, as we don't want x[None:2], right? :)

Eh? Don't we already have this?

Python 2.7.2 (default, Aug 22 2011, 13:53:27) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> range(5)[None:2]
[0, 1]

Or am I misunderstanding?

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[issue13340] list.index does not accept None as start or stop

[Amaury Forgeot d'Arc]

Amaury Forgeot d'Arc  added the comment:

str.index does accept None, though

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[issue13340] list.index does not accept None as start or stop

[Raymond Hettinger]

Raymond Hettinger  added the comment:

The API in 2.7 shouldn't be changed.
The error message can be fixed though.

Also, it is not clear that the API should change even in 3.3.  The list.index() 
method is not required to accept None.  It is not different than other APIs 
that use PyArg_ParseTuple() with an "i" field for a start, stop, or step 
argument.

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[issue13340] list.index does not accept None as start or stop

[Petri Lehtinen]

Petri Lehtinen  added the comment:

> 2) It probably should have been done in _PyEval_SliceIndex().

I saw that other code used the same approach as I used in the fix.

The comment above _PyEval_SliceIndex() suggests it's used in other
contexts too. It seems that 2.7 uses it to implement the SLICE opcode,
while in 3.x it's only used to convert slice-like arguments.

What do you suggest? Doing it in _PyEval_SliceIndex() in 2.7 is
problematic, as we don't want x[None:2], right? :)

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[issue13340] list.index does not accept None as start or stop

[Raymond Hettinger]

Raymond Hettinger  added the comment:

I think this "fix" was too hastily committed. 

1) It was an API change.
2) It probably should have been done in _PyEval_SliceIndex().

Be careful.  Don't rush to commit.  Especially for backports.

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[issue13340] list.index does not accept None as start or stop

[Raymond Hettinger]

Raymond Hettinger  added the comment:

The relevant code is in _PyEval_SliceIndex() in Python/ceval.c.

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[issue13340] list.index does not accept None as start or stop

[Petri Lehtinen]

Petri Lehtinen  added the comment:

Committed a fix for both list and tuple. I considered this a bug fix rather 
than a new feature based on discussion in #11828, especially msg133532, and 
applied the fix to 2.7 and 3.2, too.

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[issue13340] list.index does not accept None as start or stop

[Roundup Robot]

Roundup Robot  added the comment:

New changeset 0f0eda4daac7 by Petri Lehtinen in branch '2.7':
Accept None as start and stop parameters for list.index() and tuple.index()
http://hg.python.org/cpython/rev/0f0eda4daac7

New changeset 5c1fcaf3cf1c by Petri Lehtinen in branch '3.2':
Accept None as start and stop parameters for list.index() and tuple.index()
http://hg.python.org/cpython/rev/5c1fcaf3cf1c

New changeset c33aa14f4edb by Petri Lehtinen in branch 'default':
Accept None as start and stop parameters for list.index() and tuple.index().
http://hg.python.org/cpython/rev/c33aa14f4edb

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stage: needs patch -> committed/rejected
status: open -> closed

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[issue13340] list.index does not accept None as start or stop

[Alex Gaynor]

Changes by Alex Gaynor :


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[issue13340] list.index does not accept None as start or stop

[Petri Lehtinen]

Petri Lehtinen  added the comment:

The same issue exists for tuples:

>>> (1, 2, 3).index(2, None)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: slice indices must be integers or None or have an __index__ method

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nosy: +petri.lehtinen
stage:  -> needs patch
versions: +Python 3.3

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[issue13340] list.index does not accept None as start or stop

[Carl Friedrich Bolz]

New submission from Carl Friedrich Bolz :

The list.index method does not accept None as start and stop, which makes the 
error message quite confusing:

>>> [1, 2, 3].index(2, None, None)
Traceback (most recent call last):
  File "", line 1, in 
TypeError: slice indices must be integers or None or have an __index__ method

I checked this in 3.2.2 and 2.7.2. Seems similar to #12163.

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messages: 147000
nosy: Carl.Friedrich.Bolz
priority: normal
severity: normal
status: open
title: list.index does not accept None as start or stop
type: behavior
versions: Python 2.7, Python 3.2

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