New submission from Germán L. Osella Massa <[email protected]>:
The str.format() method allows index lookup on an object that supports
__getitem__(). However, negative indexes are not supported.
Examples (using Python 2.6.5):
>>> "{0[0]}".format([0, 1, 2])
'0'
>>> "{0[-1]}".format([0, 1, 2])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: list indices must be integers, not str
>>> u"{0[0]}".format([0, 1, 2])
u'0'
>>> u"{0[-1]}".format([0, 1, 2])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: list indices must be integers, not unicode
Also notice that spaces matter:
>>> "{0[ 0 ]}".format([0, 1, 2])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: list indices must be integers, not str
(The same thing happens on Python 3.1.2)
The problem is that the function get_integer() on
Objects/stringlib/string_format.h don't expect spaces or a '-' char, only
digits. If the index is not a continuous sequence of digits, it assumes that it
is a key for a dict and the index is treated as a string, and that's the cause
of the TypeError exception.
This code is the same from 2.6.5 up to trunk.
get_integer() is not very robust to parsing numbers. I'm not familiar with
CPython but perhaps the same code used in int(str) can be applied here to take
advantage of the better parsing that int() has.
----------
components: Library (Lib), Unicode
messages: 107691
nosy: Germán.L..Osella.Massa
priority: normal
severity: normal
status: open
title: String format() has problems parsing numeric indexes
type: behavior
versions: Python 2.6, Python 2.7, Python 3.1, Python 3.2
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Python tracker <[email protected]>
<http://bugs.python.org/issue8985>
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