Replace part of a matched string in python

Question

I have the following matched strings:

punctacros="Tasla"_TONTA  
punctacros="Tasla"_SONTA  
punctacros="Tasla"_JONTA  
punctacros="Tasla"_BONTA

I want to replace only a part (before the underscore) of the matched strings, and the rest of it should remain the same in each original string.

The result should look like this:

TROGA_TONTA  
TROGA_SONTA  
TROGA_JONTA  
TROGA_BONTA

Answer 1

mystring.replace('punctacross="Tasla"', 'TROGA_')

where mystring is string with those four lines. It will return string with replaced values.

Answer 2

If you want to replace everything before the first underscore, try this:

#! /usr/bin/python3

data = ['punctacros="Tasla"_TONTA',
'punctacros="Tasla"_SONTA',  
'punctacros="Tasla"_JONTA',  
'punctacros="Tasla"_BONTA',
'somethingelse!="Tucku"_CONTA']

for s in data:
    print('TROGA' + s[s.find('_'):])

Answer 3

Edit:

This should work:

from re import sub
with open("/path/to/file") as myfile:
    lines = []
    for line in myfile:
        line = sub('punctacros="Tasla"(_.*)', r'TROGA\1', line)
        lines.append(line)
with open("/path/to/file", "w") as myfile:
    myfile.writelines(lines)

Result:

TROGA_TONTA  
TROGA_SONTA  
TROGA_JONTA  
TROGA_BONTA

---

Note however, if your file is exactly like the sample given, you can replace the re.sub line with this:

line = "TROGA_"+line.split("_", 1)[1]

eliminating the need of Regex altogether. I didn't do this though because you seem to want a Regex solution.