How do I remove certain strings starting from a specific text in a text file

[qwerty3210]

Hello,
I am very new to python.
I have a text file and a python script .
I am calling the txt file in the script which fetches the data and logs into a csv file.
Now I want to remove certain data from the text file before logging to csv. how do i do that

[dwblas]

Set a boolean when the specific text is found, and then if the_boolen, remove certain strings.