regex each line.py

# read lines
lines = open('file-name.txt').readlines()

# change a specific line
# e.g. using regular expression
p = re.compile(...)
for i in range(len(lines)):
    m = p.match(lines[i])
    if m:
        # m.group(0) or m.group(1)
        # MODIFY!

# write back to this file
f = open('file-name.txt')
f.writelines(lines)
f.close()