Using Regex to Find and Replace

Question

I would like to take a text document that contains Feet+Frames values and convert them to Timecodes. For example, 0000+00 is replaced with 00:00:00:00.

I have a function to do the conversion from Feet+Frames to Timecode (16 frames per foot, framerate is 24 frames per second):

def FeetFramesToTimecode(FeetFrames):
    frames = int(FeetFrames[:4])*16+int(FeetFrames[-2:])
    return "%02d:%02d:%02d:%02d" % (frames/(3600*framerate), frames/(60*framerate)%60, frames/framerate%60, frames%framerate)

And then I have code that goes through the text file and sub's the Feet+Frame with timecode:

for line in input_document:
    found = re.search(r'\d{4}\+\d{2}', line)
    if found:
        print "%s replaces %s" % (FeetFramesToTimecode(found.group()), found.group())
        new_line = re.sub(r'\d{4}\+\d{2}', (FeetFramesToTimecode(found.group()), line)
        output_document.write(new_line)
    else:
        output_document.write(line)

So, what am I doing wrong? How do I get a function to work inside of a re.sub?

Answer 1

resub can take a second argument of a callable rather than just the replacement string.

If you pass a callable, it must take the match object.

You should also follow the python pep8 to make the python more readable (for other pythonistas)

Something like:

def feetframes_to_timecode(feetframes_match, framerate=24):
    feetframes = feetframes_match.group()
    frames = int(feetframes[:4])*16+int(feetframes[-2:])
    return "%02d:%02d:%02d:%02d" % (frames/(3600*framerate),
                                    frames/(60*framerate)%60,
                                    frames/framerate%60,
                                    frames%framerate)
# then just use:
for line in input_document:
    output_document.write(re.sub(r'\d{4}\+\d\d', feetframes_to_timecode, line))

Answer 2

Your example code has an extra '(' that does not belong. This is what the line should be:

new_line = re.sub(r'\d{4}\+\d{2}', FeetFramesToTimecode(found.group()), line)

This produced output for me like you want.