Replace String with increasing numer [SOLVED]

[bowlofred]

This works fine except for one last thing - how can I save the printed output to the same file and overwrite it?

In your code you read the data from the file into a variable with <file>.read(). You can do the opposite (on a file that has been opened for writing) with <file>.write().

# read in filedata
with open('text.txt', 'r') as file :
    filedata = file.read()

# do stuff with filedata here

# write filedata out here (overwriting the file)
with open('text.txt', 'w') as file:
    file.write(filedata)

This is a bit dangerous because for a period of time, there is no data on disk. For a production script, I'd change this to write the file to another name, then after the write has succeeded, rename the file.