How to use zip not knowing the list name

Question

I'm trying to loop through the command line arguments and open the files given. I try to read lines by using lines = file.readlines()and then use zip to combine items. But I don't know how to do it without knowing the list name. Here's my code:

import sys
import os
index = 1
while index < len(sys.argv):
    if os.path.exists(sys.argv[index]) == True:
        with open(sys.argv[index], 'r') as file:
            lines = file.readlines()
            #zip lines in files
        index = index + 1

And the contents of the file are:

file 1:

12

27

59

file 2:

21

72

95

can you post an example on the command line arguments that you expect to pass? — diegoiva, Apr 21 '18 at 00:25
Are you trying to zip together the lines of one file, or all the lines across all the files? If you have an iterable containing the things you want to zip, you can use unpacking the populate the arguments: `zip(*lines)` — Patrick Haugh, Apr 21 '18 at 00:48

diegoiva · Accepted Answer · 2018-04-21T02:58:57.723

in this approach you iterate through every argument, and append in to a list, at the end of each file it will apend to a new list, and you'll end up with a list of lists

import sys
import os
container = []
for document in sys.argv[1:]:
    if os.path.exists(document):
        aux = []
        with open(document, 'r') as file:
            for line in file:
                aux.append(line.replace('\n',''))
    container.append(aux)
print(*zip(*container))

Then you can just unpack the list and zip it, I manually replace the jump of line, do whatever you want with that. ;)

File 1 contains

File 2 contains

Input

python test.py test1.txt test2.txt

Output

('7', '11') ('1', '12') ('3', '13') ('5', '14') ('6', '15')

Edit

in this line "print(*zip(*container))", we are unpacking the container which is a list that has lists on it, when we zip it, as you may know when you zip something, a zip object is created, which is an iterable, in order to "unzip" it and to represent it as a set of tupples you use the * (starred expression), which unpacks it for example:

>>> a = zip([1,2,3,4,5], [5,4,3,2,1])
>>> print(a)
<zip object at 0x00000219ECE8C408>
>>> print(*a)
(1, 5) (2, 4) (3, 3) (4, 2) (5, 1)

Thanks for your help. But what does the *zip(*container) mean? — Jesse, Apr 21 '18 at 01:16

How to use zip not knowing the list name

1 Answers1