Python regex example

Question

If I want to replace a pattern in the following statement structure:

cat&345;
bat &#hut;

I want to replace elements starting from & and ending before (not including ;). What is the best way to do so?

Good question, but please show also what you have been trying :) — icedwater
– icedwater, Commented Jun 28, 2013 at 2:09

Mark Tolonen · Accepted Answer · 2013-06-28 02:20:43Z

1

Including or not including the & in the replacement?

>>> re.sub(r'&.*?(?=;)','REPL','cat&345;')           # including
'catREPL;'
>>> re.sub(r'(?<=&).*?(?=;)','REPL','bat &#hut;')    # not including
'bat &REPL;'

Explanation:

Although not required here, use a r'raw string' to prevent having to escape backslashes which often occur in regular expressions.
.*? is a "non-greedy" match of anything, which makes the match stop at the first semicolon.
(?=;) the match must be followed by a semicolon, but it is not included in the match.
(?<=&) the match must be preceded by an ampersand, but it is not included in the match.

answered Jun 28, 2013 at 2:20

Mark Tolonen

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aaronman · Accepted Answer · 2013-06-28 02:09:51Z

1

Here is a good regex
import re result = re.sub("(?<=\\&).*(?=;)", replacementstr, searchText)
Basically this will put the replacement in between the & and the ;

answered Jun 28, 2013 at 2:09

aaronman

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John Szakmeister · Accepted Answer · 2013-06-28 02:24:40Z

0

Maybe go a different direction all together and use HTMLParser.unescape(). The unescape() method is undocumented, but it doesn't appear to be "internal" because it doesn't have a leading underscore.

answered Jun 28, 2013 at 2:24

John Szakmeister

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dawg · Accepted Answer · 2013-06-28 02:38:17Z

0

You can use negated character classes to do this:

import re

st='''\
cat&345;
bat &#hut;'''

for line in st.splitlines():
    print line
    print re.sub(r'([^&]*)&[^;]*;',r'\1;',line)

answered Jun 28, 2013 at 2:38

dawg

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