Generate a large size of CSV file was filled random values. This script generates around 250MB size of the file. You can adjust two parameters `row` and `col` to generate the file which has desirable size.

generate_L_size_csv.py

import csv
import random

def generate_random_array(row, col):
    a = []
    for i in range(col):
        l = [i]
        for j in range(row):
            l.append(random.random())
        a.append(l)
    return a

if __name__ == '__main__':
    row = 10
    col = 1500000

    array = generate_random_array(row, col)

    f = open('sample.csv', 'w')
    w = csv.writer(f, lineterminator='\n')
    w.writerows(array)
    f.close()