How to substitute several regex in Python?

Question

I would like to loop on every lines from a .txt file and then use re.sub method from Python in order to change some contents if there is a specific pattern matcing in this line.

But how can I do that for two different pattern in the same file ?

For example, here's my code :

file = open(path, 'r')
output = open(temporary_path, 'w')

for line in file:
    out = re.sub("patternToChange", "patternToWrite", line) #Here I would like to also do the same trick with "patternToChange2 and patternToWrite2 also in the same file
    output .write(out)

Do you have any ideas ?

Could you please provide a very basic example of input and expected output? I couldn't quite catch the idea. — Celius Stingher, Aug 30 '19 at 15:50
Can you provide a few sample lines from the file and also describe what you wish to find and what you wish to replace? From a pure stance, you're current code **will** literally find `patternToChange` and replace it with `patternToWrite`. — MonkeyZeus, Aug 30 '19 at 15:51
Can't you just run `re.sub` again, but taking `out` as its input, and using your new patterns? If you saved the result back to `out`, you wouldn't need to make any other changes. — Scott Hunter, Aug 30 '19 at 15:54
Does the python syntax allow for `re.sub(...).sub(...)` in one line? If not, Scott's idea is correct where you would do `out = re.sub(pattern1, write1, line)` then `out = re.sub(pattern2, write2, out)` — dvo, Aug 30 '19 at 16:00
Why don't you read the whole file into a string, do the 2 sub's on it, then write it back. It's the cleanest way. It's very rare a regex doesn't apply to spanned lines... — , Aug 30 '19 at 16:41

Nick Reed · Answer 1 · 2019-08-30T18:19:32.520

I think it'd be best to apply all of your regex(es) to the string, one at a time, before you write it to the file. Maybe something like this?

for line in file:
    out = re.sub('patternToChange', 'patternToWrite', line)
    out2 = re.sub('patternToChange2', 'patternToWrite2', out)
    output.write(out2)

The above code worked fine for me - try it here if you'd like. Also, be sure to .close() your files when you're done, or the output might not show up in them.

How to substitute several regex in Python?

1 Answers1