Python Regex Question

Question

I have an end tag followed by a carriage return line feed (x0Dx0A) followd by one or more tabs (x09) followed by a new start tag .

Something like this:

</tag1>x0Dx0Ax09x09x09<tag2> or </tag1>x0Dx0Ax09x09x09x09x09<tag2>

What Python regex should I use to replace it with something like this:

</tag1><tag3>content</tag3><tag2>

Thanks in advance.

Answer 1

The regex for a generic version of this (i.e. will match regardless of the #s listed with the tags) is:

(</tag\d+>)x0Dx0A(?:x09)+(<tag\d+>)

You can use this in what cjrh provided to do the replacement, as follows:

import re
input   = '</tag1>x0Dx0Ax09x09x09<tag2> or </tag1>x0Dx0Ax09x09x09x09x09<tag2>'
pattern = '(</tag\d+>)x0Dx0A(?:x09)+(<tag\d+>)'
replace = r'\1<tag3>content</tag3>\2'
output  = re.compile(pat, re.M | re.S).sub(repl,input)

Answer 2

Here is code for something like what you say that you need:

>>> import re
>>> sample = '</tag1>\r\n\t\t\t\t<tag2>'
>>> sample
'</tag1>\r\n\t\t\t\t<tag2>'
>>> pattern = '(</tag1>)\r\n\t+(<tag2>)'
>>> replacement = r'\1<tag3>content</tag3>\2'
>>> re.sub(pattern, replacement, sample)
'</tag1><tag3>content</tag3><tag2>'
>>>

Note that \r\n\t+ may be a bit too specific, especially if production of your input is not under your control. It may be better to adopt the much more general \s* (zero or more whitespace characters).

Using regexes to parse XML and HTML is not a good idea in general ... while it's hard to see a failure mode here (apart from elementary errors in getting the pattern correct), you might like to tell us what the underlying problem is, in case some other solution is better.