How to replace a character and overwrite the original file

Question

I'm trying to change the | symbol with the _ on a text of a file and overwrite the result.

The text of my file is something like:

#Hello there|this is my text_to_modify

So as you can see the _ is already present is some parts of the text but I want to change only the | symbol.

The code I wrote is:

import re

with open(my_file,'r+') as f:
    text = f.read()
    text = re.sub('|', '_', text)
    f.seek(0)
    f.write(text)
    f.truncate()
    f.close()

and the output is:

#Hello_there|this_is_my_text_to_modify

What can I do? Thanks in advance for the answers.

Answer 1

You need to escape the pipe symbol:

text = re.sub('\|', '_', text)

| has a special meaning in regular expressions ('or') and has to be escaped to be used literally. I don't understand how you got the output you reported, because what your regex '|' is basically saying is, 'match nothing or nothing and replace it with an underscore', so your output should have underscores between all of the characters (where 'nothing' is).

I recommend you take a good look at the excellent Python regex documentation.

As a side note, the way you overwrite the original file is very dangerous: If you mess something up, you lose all the content from the original file. Better output into a new file.