using numpy.save code example

Example: numpy array storing in file by python

# long arrays can be stored in csv files far more efficiently
import numpy as np
import csv

# uploading arrays in a csv file
arr1 = [i for i in range(500)]
arr2 = [i for i in range(1000)]
arr3 = [i for i in range(2000)]
# you can write('w') or append('a')
with open('record.csv', 'a') as record_append:
    np.savetxt(record_append, np.asarray([arr1]), delimiter=',')
    np.savetxt(record_append, np.asarray([arr2]), delimiter=',')
    np.savetxt(record_append, np.asarray([arr3]), delimiter=',')

# downloading them from the csv file
two_dim_arr = []  # each line of the file is an array element
with open('record.csv', 'r') as record_read:
    reader = csv.reader(record_read)
    for i, each_arr in enumerate(reader):
        two_dim_arr.append([eval(each) for each in each_arr])
        
# printing the arrays in lines
for each_line in two_dim_arr:
  print(each_line)