[Python-ideas] Python 2's re module should take longs

[Steven D'Aprano]

On Tue, Sep 30, 2014 at 09:57:44PM +0200, Antoine Pitrou wrote:
> On Tue, 30 Sep 2014 12:16:13 -0500
> Ryan Gonzalez <rymg19 at gmail.com> wrote:
> > This works:
> > 
> > re.search('(abc)', 'abc').group(1)
> > 
> > but this doesn't:
> > 
> > re.search('(abc)', 'abc').group(1L)
> > 
> > The latter raises "IndexError: no such group". Shouldn't that technically
> > work?
> 
> Yes, it's a bug.  Feel free to open an issue.

I'm not so sure that it's a bug. Should .group(1.0) work? That also is 
numerically equal to 1.

MatchObject.group does not necessarily have to obey the semantics of 
list.index or dict.__getitem__. Just because ['a', 'b'].index(1L) and 
{1: 'b'}[1.0] both return 'b' doesn't force .group() to do the same.

The documentation for .group is underspecified, and perhaps TypeError 
would be a more appropriate error rather than IndexError, but IndexError 
is consistent with other bad arguments:

py> re.search('(abc)', 'abc').group([])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: no such group

So I don't think this is a bug, I think it is just an unfortunate choice 
of misleading exception type.

The re module goes back to at least 1.5, and as far as I can tell, 
.group has never accepted longs. (I have tested it on 2.4 through 2.7, 
and 1.5, and it fails with all of them.) So this is a long-established 
restriction on the argument.

(Another restriction is that a maximum of 99 groups are supported, so 
there are no cases where a long is needed.)

Allowing longs is a new feature, not a bug fix.

Since 2.7 is bug-fix only mode, and this fix is unneeded in 3.x, there 
is no point in raising an issue to the tracker. 



-- 
Steven