Python: Choose random line from file, then delete that line

Question

I\'m new to Python (in that I learned it through a CodeAcademy course) and could use some help with figuring this out.

I have a file, \'TestingDeleteLines.txt\', tha

Answer 1

I have a file, 'TestingDeleteLines.txt', that's about 300 lines of text. Right now, I'm trying to get it to print me 10 random lines from that file, then delete those lines.

#!/usr/bin/env python
import random

k = 10
filename = 'TestingDeleteLines.txt'
with open(filename) as file:
    lines = file.read().splitlines()

if len(lines) > k:
    random_lines = random.sample(lines, k)
    print("\n".join(random_lines)) # print random lines

    with open(filename, 'w') as output_file:
        output_file.writelines(line + "\n"
                               for line in lines if line not in random_lines)
elif lines: # file is too small
    print("\n".join(lines)) # print all lines
    with open(filename, 'wb', 0): # empty the file
        pass

It is O(n**2) algorithm that can be improved if necessary (you don't need it for a tiny file such as your input)