Editing text in a file using python

Question

I have a text file (file1.txt) containing pattern like this.

****
****
****
****

I want to replace it by **. I can use command something like this sed -i 's/\*{4}/**/' file1.txt in linux to get in place replacement. But I want to do this operation in Windows environment using python script.

import re
with open ('file1.txt') as fil1:
     for line in fil1:
         re.sub('^\*{3}[*]*','**',line)

But this script does not seem to replace **** by ** in place in the file. How can I get in place file replacement (similar to sed command) in python?

Edit:

I do not want to read file line by line, replace text and write the line into another file. I want to do something like sed -i to do in place file replacement in python using regular expressions.

The problem is that you're not writing anything. You are just reading from the file to the variable line and change the variable. — klutt, Jul 23 '17 at 18:31
Possible duplicate of [Search and replace a line in a file in Python](https://stackoverflow.com/questions/39086/search-and-replace-a-line-in-a-file-in-python) — klutt, Jul 23 '17 at 18:33
You _cannot_ get any kind of 'in-place' changes in a file. You only can read from it and write into it. And all of this has to be done explicitly. — ForceBru, Jul 23 '17 at 18:33
@dfs3w, no, it doesn't. Also, given that you ignore its return value, in your code it doesn't do anything at all. — ForceBru, Jul 23 '17 at 18:35
OK. How can I do in place replacement in python using regular expressions? — dfs3w, Jul 23 '17 at 18:50

cs95 · Accepted Answer · 2017-07-23T19:08:52.867

0

You're trying to edit the file inlace, but you open the file in read mode, so it is not open for writing.

Furthermore, you are calling re.sub which returns a new string that you do not capture and attempt to write.

Editing a file inplace is challenging with the builtin functions, but is made easy with the fileinput module:

import fileinput

with fileinput.FileInput('file1.txt', inplace=True) as fil1:
    for line in fil1:
        text = re.sub('^\*{3}[*]*','**', line.rstrip()).strip()
        if text:
            print(text) # inside the `with` clause, print writes to the file automatically

edited Jul 23 '17 at 19:08

answered Jul 23 '17 at 18:50

cs95

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It inserts blank like in the last line of the file. Do you know how to get rid of that? – dfs3w Jul 23 '17 at 19:07
@dfs3w Your input file probably has that. Check my edit? And if it helps, do mark it accepted :) – cs95 Jul 23 '17 at 19:09

Editing text in a file using python

1 Answers1