• I have a file called data.txt containing lines of data:

    This is line one
    This is line two 
    This is line three 
    This is line four 
    This is line five 
    This is line six 
    This is line seven
    


    I have the following code:

    with open('data.txt', 'r') as f:
        for x, line in enumerate(f):
            if x == 3:
                print(line)
    In this case it only prints
    

    “This is line four”.
    I do understand why but how do I take it from here and have it print the lines 4, 7, 10, 13, …?

  • Cyberian's Gold

    Demo:

    data.txt:

    line1
    line2
    line3
    line4
    line5
    line6
    line7
    line8
    line9
    line10
    line11
    line12
    line13
    

    Code:

    from itertools import islice
    
    with open('data.txt') as f:
        for line in islice(f, 3, None, 3):
            print line,  # Python3: print(line, end='')
    

    Produces:

    line4
    line7
    line10
    line13
    

    Reff

  • Cyberian's Gold

    Demo:

    data.txt:

    line1
    line2
    line3
    line4
    line5
    line6
    line7
    line8
    line9
    line10
    line11
    line12
    line13
    

    Code:

    from itertools import islice
    
    with open('data.txt') as f:
        for line in islice(f, 3, None, 3):
            print line,  # Python3: print(line, end='')
    

    Produces:

    line4
    line7
    line10
    line13
    

    Reff

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