Python file iteration and nested for loops

Question

I have a python program where I pass in a file, I read this file and then split the line at a colon. I then print both these parts, do some checking on it and pass it into a function where if its a match it prints out the match then returns. However I cannot figure out how to then get the next line in my file, the program currently just keeps going over and over on that one line

with open(myfile,'r') as hf:
for l in hf:
    part1 = l.split(":")[0].strip()
    part2 = l.split(":")[1].strip()


    print part1
    print part2
    print "**************"

    for file in filenames:
        print "Starting " + file
        if ".txt" in file or ".lst" in file:
            file = os.path.join(mypath, file)
            with open(file,'r') as f:
                for line in f:
                    for word in line.split():
                        ThenWord(part2,word)

I have tried break, continue and else, along with next() but I can't seem to get it working, or it's in the wrong place. How would I get the next line from the open file and then start the for loop again to split at the colon, line 3 and 4.

EDIT: I have added in 2 breaks, but the files I try and match the word to (for file in filenames) only reads the first file then moves onto the next line from myfile.

with open(myfile,'r') as hf:
for l in hf:
    part1 = l.split(":")[0].strip()
    part2 = l.split(":")[1].strip()


    print part1
    print part2
    print "**************"

    for file in filenames:
        print "Starting " + file
        if ".txt" in file or ".lst" in file:
            file = os.path.join(mypath, file)
            with open(file,'r') as f:
                for line in f:
                    for word in line.split():
                        ThenWord(part2,word)
                        break
                break


def ThenWord(salt,word):
    salted = salt + word
    m = hashlib.md5()
    m.update(salted)
    if m.hexdigest() == hash:
        print "************ " + hash + " ************"
        print "******* Enough said - " + word + " ******* "
        return

I want it so that once it has found a match, it moves on to the next hash in the file (myfile) without scanning through every other file in filenames.

the line in f is a different part of the program, i am attempting to get the next line of with open(myfile,'r') as hf: for l in hf: — Hoohaee
– Hoohaee, Commented Aug 2, 2017 at 16:10
What happens if you comment out most of the code in the for loop ? — Gribouillis
– Gribouillis, Commented Aug 2, 2017 at 16:26
it prints out everything in my file using the 3 print statements above. so its something with the other for loop/the return from the function then. — Hoohaee
– Hoohaee, Commented Aug 2, 2017 at 16:31
A break exits the innermost loop that contains it. In your case the second break exits for file in filenames. Blocs starting with if or with are not loops. — Gribouillis
– Gribouillis, Commented Aug 2, 2017 at 16:40

Gribouillis · Accepted Answer · 2017-08-02 17:03:21Z

1

It finally appears that your problem is to exit a deeply nested loop. A possible solution is to raise an exception

class MatchFoundException(Exception):
    pass


with open(myfile, 'r') as hf:
    for ...
        ...

        try:
            for file in filenames:
                ...
                        for word in line.split():
                            if ThenWord(part2, word):
                                raise MatchFoundException(('Found', part2, word))
        except MatchFoundException:
            # do something
        else:
            # optionally do something

You need to change ThenWord to return True or False for example.

answered Aug 2, 2017 at 17:03

Gribouillis

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3 Comments

Oluwafemi Sule Over a year ago

What's the need to raise an Exception here?

Gribouillis Over a year ago

@OluwafemiSule It's not required, it's only a shortcut to exit several nested loops.

Oluwafemi Sule Over a year ago

I noticed. Another way is to go is to initialize a name before entering any of the loops that tracks if a match was found. I like how you wrote it better.

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