How to input a regex in string.replace?

Question

I need some help on declaring a regex. My inputs are like the following:

this is a paragraph with<[1> in between and then there are cases ..         


        

Answer 1

import os, sys, re, glob

pattern = re.compile(r"\<\[\d\>")
replacementStringMatchesPattern = "<[1>"

for infile in glob.glob(os.path.join(os.getcwd(), '*.txt')):
   for line in reader: 
      retline =  pattern.sub(replacementStringMatchesPattern, "", line)         
      sys.stdout.write(retline)
      print (retline)

Answer 2

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

Answer 3

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

Answer 4

replace method of string objects does not accept regular expressions but only fixed strings (see documentation: http://docs.python.org/2/library/stdtypes.html#str.replace).

You have to use re module:

import re
newline= re.sub("<\/?\[[0-9]+>", "", line)

Answer 5

The easiest way

import re

txt='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>'

out = re.sub("(<[^>]+>)", '', txt)
print out

Answer 6

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!