Iterative regex in Python: find and replace

Question

This is one of those "I'd know how to do it in C" type questions. :p I'm asking this as similar questions in SO don't have a particular aspect I'm looking for.

I'm essentially looking to find and replace items that also have possessive forms. So if there is a "rabbit" in the list, and also a "rabbit's", then replace "rabbit" with a series of asterisks.

Something along the lines of:

#!/usr/bin/env python

import re

text = open("list.txt", "w")

for line in text:
        test = line
        if re.match(test+"'", line) or re.match(test+"'s", line):
            line = "****"

However, this clearly won't work as the for each mechanism makes line be used for both iteration and pattern matching.

test = line and then re.match(test+"'", line), how is that supposed to work? — Benjamin Toueg
– Benjamin Toueg, Commented Dec 15, 2014 at 12:44
line = "****" does nothing in this case, variable is recreated in the loop for each element. — Rusty
– Rusty, Commented Dec 15, 2014 at 12:52

Ewan · Accepted Answer · 2014-12-15 12:47:54Z

2

with open('file.txt') as f:
    # Remove the \n characters at the end of each line
    all_lines = [x.strip() for x in f.readlines()]
    for line in all_lines:
        # Check for presence of word' or word's 
        if line+"'" in all_lines or line+"'s" in all_lines:
            print('****')
        else:
            print(line)

It's worth noting that this is quite a brute force way of doing and for huge lists will take a bit longer (it loads the file into memory) but should give you an idea.

answered Dec 15, 2014 at 12:47

Ewan

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Hackaholic · Accepted Answer · 2014-12-15 12:54:39Z

1

you can use str.endswith:

text = open("list.txt", "r")

for line in text:
    test = line.strip()
    if test.endswith("'s"):
        line = "****"

Here i have explained why your code is not going to work:

replace this:

test = line

to:

test = line.strip()   # to remove new line character

so your test will be rabbit\n', if you don't remove newline character

you also need to open file on read mode

text = open("list.txt",'r')

you match is not going to work, think of it:

suppose test="rabbit's"

    test+"'" will give you `rabbit's'`

edited Dec 15, 2014 at 12:54

answered Dec 15, 2014 at 12:37

Hackaholic

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