sqlite3.Row doesn't support slice indexes

[xapple]

BPO	13583
Nosy	@pitrou, @serhiy-storchaka
Files	sqlrowslice.patch: Patch for implementing slices in sqlite3.Row issue13583.patch sqlite3_slicing_demo.py sqlite3_row_slice.patch

^{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 = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2015-03-31.10:36:54.897>
created_at = <Date 2011-12-11.21:45:47.766>
labels = ['extension-modules', 'type-feature']
title = "sqlite3.Row doesn't support slice indexes"
updated_at = <Date 2015-03-31.10:36:54.896>
user = 'https://bugs.python.org/xapple'

bugs.python.org fields:

activity = <Date 2015-03-31.10:36:54.896>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2015-03-31.10:36:54.897>
closer = 'serhiy.storchaka'
components = ['Extension Modules']
creation = <Date 2011-12-11.21:45:47.766>
creator = 'xapple'
dependencies = []
files = ['23919', '35070', '35071', '38379']
hgrepos = []
issue_num = 13583
keywords = ['patch', 'needs review']
message_count = 9.0
messages = ['149251', '149871', '217343', '217344', '233840', '237462', '239172', '239680', '239681']
nosy_count = 6.0
nosy_names = ['ghaering', 'pitrou', 'jesstess', 'python-dev', 'xapple', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue13583'
versions = ['Python 3.5']

[xapple]

When using the sqlite3.Row object as a row factory, one can access the resulting rows by index (such as row[1]) or by name (such as row['b']). However, the slice functionality is lost, as doing row[0:2] raises the error:

"slices not implemented, yet"

Here is a patch that fixes this, I implemented it and I added the corresponding unit test.

[pitrou]

Thanks for the patch. Two things:

• there is a compilation warning using gcc:

/home/antoine/cpython/default/Modules/_sqlite/row.c: In function ‘pysqlite_row_subscript’:
/home/antoine/cpython/default/Modules/_sqlite/row.c:128:26: attention : passing argument 1 of ‘PySlice_GetIndicesEx’ from incompatible pointer type

• you can use assertEqual to avoid defining the error message yourself

[jesstess]

Thanks for the ticket and patch, xapple!

I updated the patch to address the compiler warning and use assertEqual.

While testing, I noticed that slicing with steps wasn't supported, so I expanded the sqlite3.Row slicing code to support steps, and added some additional tests.

The slicing code in Modules/_sqlite/row.c:pysqlite_row_subscript is unfortunately pretty redundant with the slicing code in Objects/tupleobject.c. It'd be better to either be able to factor the code from both into a function (but I couldn't see how to do this without making it part of the public API), or have tuple, sqlite.Row, etc. implement a shared slicing interface. Perhaps we should defer that decision to a future ticket, though.

Note that even after this patch, sqlite.Row instances don't support negative indices.

• This patch passes make patchcheck.
• The full test suite passes with this patch.
• There are no build warnings related to the patch.

[jesstess]

I've also uploaded a short script that sets up an in-memory sqlite database that fetches Rows, for easy manual testing.

[serhiy-storchaka]

May be just use PyObject_GetItem(self->data, idx)?

[serhiy-storchaka]

Here is a patch with much simpler implementation.

[serhiy-storchaka]

Could you look at the patch Gerhard?

[python-dev]

New changeset e47f520eb756 by Serhiy Storchaka in branch 'default':
Issue bpo-13583: sqlite3.Row now supports slice indexing.
https://hg.python.org/cpython/rev/e47f520eb756

[serhiy-storchaka]

The implementation can be much simpler, but in any case thank you for your patches Lucas and Jessica.