up vote 0 down vote favorite

I need some help on declaring some regex. my inputs as as such

this is a paragraph with<[1> in between</[1> and then there are cases ... where the<[99> number ranges from 1-100</[99>. 
and there are many other lines in the txt files
with<[3> such tags </[3>

the required output should be

this is a paragraph with in between and then there are cases ... where the number ranges from 1-100. 
and there are many other lines in the txt files
with such tags

I've tried the code

#!/usr/bin/python
import os, sys, re, glob
for infile in glob.glob(os.path.join(os.getcwd(), '*.txt')):
    for line in reader: 
        line2 = line.replace('<[1> ', '')
        line = line2.replace('</[1> ', '')
        line2 = line.replace('<[1>', '')
        line = line2.replace('</[1>', '')

        print line

i've also tried, but seems like i'm using the wrong regex syntax:

    line2 = line.replace('<[*> ', '')
    line = line2.replace('</[*> ', '')
    line2 = line.replace('<[*>', '')
    line = line2.replace('</[*>', '')

Can someone help me with this? i dont want to hard code the replace from 1 to 99. thanks

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3 Answers

up vote 8 down vote accepted

This tested snippet should do it:

import re
line = re.sub(r"</?\[\d+>", "", line)

Edit: Here's a commented version explaining how it works:

line = re.sub(r"""
  (?x) # Use free-spacing mode.
  <    # Match a literal '<'
  /?   # Optionally match a '/'
  \[   # Match a literal '['
  \d+  # Match one or more digits
  >    # Match a literal '>'
  """, "", line)

Regexes are fun! But I would strongly recommend spending an hour or two studying the basics. For starters, you need to learn which characters are special: "metacharacters" which need to be escaped (i.e. with a backslash placed in front - and the rules are different inside and outside character classes.) There is an excellent online tutorial at: www.regular-expressions.info. The time you spend there will pay for itself many times over. Happy regexing!

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care to explain the regex? – 2er0 Apr 14 '11 at 6:35
yep it works!! thanks but can you explain the regex in brief? – 2er0 Apr 14 '11 at 6:39
up vote 4 down vote

str.replace() does fixed replacements. Use re.sub() instead.

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1  
Also worth noting that your pattern should look something like "</{0-1}\d{1-2}>" or whatever variant of regexp notation python uses. – bdares Apr 14 '11 at 4:05
up vote 1 down vote

don't have to use regular expression (for your sample string)

>>> s
'this is a paragraph with<[1> in between</[1> and then there are cases ... where the<[99> number ranges from 1-100</[99>. \nand there are many other lines in the txt files\nwith<[3> such tags </[3>\n'

>>> for w in s.split(">"):
...   if "<" in w:
...      print w.split("<")[0]
...
this is a paragraph with
 in between
 and then there are cases ... where the
 number ranges from 1-100
.
and there are many other lines in the txt files
with
 such tags
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