[issue2650] re.escape should not escape underscore

[Russ Cox]

Russ Cox <rsc at swtch.com> added the comment:

> Lorenz's patch uses a set, not a list for special characters.  Set 
> lookup is as fast as dict lookup, but a set takes less memory because it 
> does not have to store dummy values.  More importantly, use of frozenset 
> instead of dict makes the code clearer.  On the other hand, I would 
> simply use a string.  For a dozen entries, hash lookup does not buy you 
> much.
> 
> Another nit: why use "\\%c" % (c) instead of obvious "\\" + c?
> 
> Finally, you can eliminate use of index and a temporary list altogether 
> by using a generator expression:
> 
> ''.join(("\\" + c if c in _special else '\\000' if c == "\000" else c),
>         for c in pattern)

The title of this issue (#2650) is "re.escape should not escape underscore",
not "re.escape is too slow and too easy to read".

If you have an actual, measured performance problem with re.escape,
please open a new issue with numbers to back it up. 
That's not what this one is about.

Thanks.
Russ

__________________________________
Tracker <report at bugs.python.org>
<http://bugs.python.org/issue2650>
__________________________________