How can I use nested for loops in Python-3.x to print from a text file one line at a time, x number of cycles?

Question

I am attempting to print from a text file one line at a time, however many cycles I require. I am stuck here:

    def do():
        i = 0
        for i in range(int(mlt)):
            file = open('/some/dir/text.txt' , 'r')
            for line in file:
                linenumber = file.readline()
                time.sleep(1)
                print(linenumber)

    mlt = input('number of cycles')
    do()

This outputs to:

    line2

    line4

    line6

    line8

    line10

    line2

    line4
    ....

When I require:

    line1

    line2

    line3

    line4

    line5

    line6

    line7

    line8

    line9

    line10

    line1

    line2

    line3
    ...

I would greatly appreciate if someone could explain to me what it is I am doing wrong.

print adds a carriage return. try print(linenumber.strip('\n')) or ('\r') depending on what sort of crs your system is using. — tlastowka
– tlastowka, Commented Oct 26, 2015 at 3:15

dstudeba · Accepted Answer · 2015-10-26 03:19:49Z

1

for line in file: and linenumber = file.readline() are doing the same thing which is why you are getting every second line. Try the following:

     for line in file:
            time.sleep(1)
            print(line)

answered Oct 26, 2015 at 3:19

dstudeba

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TigerhawkT3 · Accepted Answer · 2015-10-26 03:19:12Z

0

You're iterating over the file with for line in file:, but then in each iteration you grab the next line with readline(), resulting in printing every other line. The double-spacing is because print() has a default end of a newline. To fix this, simply print every line in the file with no extra characters:

def do(num):
    for i in range(num):
        with open('/some/dir/text.txt' , 'r') as file:
            for line in file:
                time.sleep(1)
                print(line, end='')

mlt = input('number of cycles')
do(int(mlt))

I've also refactored your code a bit so the function takes an argument representing the number of times it should loop.

answered Oct 26, 2015 at 3:19

TigerhawkT3

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