Filtering by values in text list in Python

Question

I have a Python script written where I'm trying to filter some text files and compare them to another text file, however I'm struggling to find a solution.

below | 1

above | 2

above | 3

above | 4

above | 5

below | 6

below | 7

below | 8

below | 9

below | 10

below | 11

below | 12

above | 13

below | 14

below | 15

below | 16

below | 17

below | 18

below | 19

below | 20

below | 21

...

I have this file listing video frames and whether they're above or below a defined threshold.

Additionally, I have a list of those 'above' threshold frames, and a user-defined value tagged (either x, y or z) to each. Unfortunately the numbers in this list do not correspond to the initial above-or-below frame number, but instead are just a numbered list.

y | 1
x | 2
x | 3
y | 4
z | 5
z | 6
y | 7
z | 8
y | 9
y | 10
x | 11
x | 12
y | 13
x | 14
x | 15
x | 16
x | 17
x | 18
y | 19
x | 20
z | 21

I want to combine these two such that the x, y or z values of the above frames replace the 'above' tag in the other script, like this:

below | 1

y | 2

x | 3

x | 4

y | 5

below | 6

below | 7

below | 8

below | 9

below | 10

below | 11

below | 12

z | 13

below | 14

below | 15

below | 16

below | 17

below | 18

below | 19

below | 20

below | 21

However I can't get my head round how to iterate through the list to achieve this. Should I be storing values in a dictionary and iterating over those? Any help would be much appreciated. I've tried using some for loops and with open statements to try it but I can't get my head round how to iterate through it:

 with open((selectedvideostring + 'combinedfiles.txt'), 'w') as combinedfile:
    with open((selectedvideostring + 'aboveorbelow.txt'), 'r') as aboveorbelowfile:
        for line in aboveorbelowfile:
            if 'above' in line:
                with open((selectedvideostring + 'xyzfile.txt'), 'r') as xyzfile:
                    for line in xyzfile:
                        if 'x' in line:
                            combinedfile.write("x" + '|' + str(int(cap.get(1))))

                        elif 'y' in line:
                            combinedfile.write("y" + '|' + str(int(cap.get(1))))

                        if 'z' in line:
                            combinedfile.write("z" + '|' + str(int(cap.get(1))))

            elif 'below' in line:
                combinedfile.write("below" + '|' + str(int(cap.get(1))))

Thanks!

Please paste the content of those files into your question so we don't have to re-type all that stuff in order to test a possible solution. — tobias_k
– tobias_k, Commented Apr 24, 2017 at 10:36
Right, pasted the content, and the rubbish code I have so far! — KittenMittons
– KittenMittons, Commented Apr 24, 2017 at 10:54

tobias_k · Accepted Answer · 2017-04-24 11:11:29Z

1

Instead of opening and iterating the xyz file inside of the outer above-or-below file loop, you should open both files at once. Files are iterators, so you can use a for loop to iterate the lines in the above-or-below file, and use next to just get the next line from the xyz file whenever you encounter a "above" entry.

with open("aboveorbelow.txt") as aob, open("xyzfile.txt") as xyz:
    for line in aob:
        if line.startswith("above"):
            ab, c = line.split(" | ")
            d, _ = next(xyz).split(" | ")
            print(" | ".join((d, c)))
        elif line.startswith("below"):
            print(line)

(Using print for simplicity of testing, but of course the same works with an output file.)

answered Apr 24, 2017 at 11:11

tobias_k

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4 Comments

KittenMittons Over a year ago

Thanks for the help! One small issue, implementing that code in my program I'm getting an error, reading 'StopIteration', throwing the error on the line d, _ = next(xyz).split(" | ")

tobias_k Over a year ago

@KittenMittons In this case, there are not enough xyz values in your second file. You could use next with a default value, if a useable default exists, e.g. next(xyz, "UNKNOWN | 0").split(" | ").

KittenMittons Over a year ago

Thanks very much - that has stopped the StopIteration issue - when I use those print statements as above it outputs exactly as I want it, however when I try to write those lines to a new output file, it completes with no errors, yet no file exists - I'll add the code I'm using as implemented as an edit in the original question now, I must be doing something wrong

KittenMittons Over a year ago

Never mind, it was me not saving the correct file path - I've sorted it, thanks so much for all your help!!

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