[Tutor] Removing control characters

[Dinesh B Vadhia]

At the bottom of the link http://code.activestate.com/recipes/303342/ there are list comprehensions for string manipulation ie.

import string

str = 'Chris Perkins : 224-7992'
set = '0123456789'
r = '$'

# 1) Keeping only a given set of characters.

print  ''.join([c for c in str if c in set])

> '2247992'

# 2) Deleting a given set of characters.

print  ''.join([c for c in str if c not in set])

> 'Chris Perkins : -'

The missing one is

# 3) Replacing a set of characters with a single character ie.

for c in str:
    if c in set:
        string.replace (c, r)

to give

> 'Chris Perkins : $$$-$$$$'

My solution is:

print ''.join[string.replace(c, r) for c in str if c in set]

But, this returns a syntax error.  Any idea why?

Ta!

Dinesh




From: Kent Johnson 
Sent: Thursday, February 19, 2009 8:03 AM
To: Dinesh B Vadhia 
Cc: tutor at python.org 
Subject: Re: [Tutor] Removing control characters


On Thu, Feb 19, 2009 at 10:14 AM, Dinesh B Vadhia
<dineshbvadhia at hotmail.com> wrote:
> I want a regex to remove control characters (< chr(32) and > chr(126)) from
> strings ie.
>
> line = re.sub(r"[^a-z0-9-';.]", " ", line)   # replace all chars NOT A-Z,
> a-z, 0-9, [-';.] with " "
>
> 1.  What is the best way to include all the required chars rather than list
> them all within the r"" ?

You have to list either the chars you want, as you have done, or the
ones you don't want. You could use
r'[\x00-\x1f\x7f-\xff]' or
r'[^\x20-\x7e]'

> 2.  How do you handle the inclusion of the quotation mark " ?

Use \", that works even in a raw string.

By the way string.translate() is likely to be faster for this purpose
than re.sub(). This recipe might help:
http://code.activestate.com/recipes/303342/

Kent
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