long arrays storing in file python

1# long arrays can be stored in csv files far more efficiently
2import numpy as np
3import csv
4
5# uploading arrays in a csv file
6arr1 = [i for i in range(500)]
7arr2 = [i for i in range(1000)]
8arr3 = [i for i in range(2000)]
9# you can write('w') or append('a')
10with open('record.csv', 'a') as record_append:
11    np.savetxt(record_append, np.asarray([arr1]), delimiter=',')
12    np.savetxt(record_append, np.asarray([arr2]), delimiter=',')
13    np.savetxt(record_append, np.asarray([arr3]), delimiter=',')
14
15# downloading them from the csv file
16two_dim_arr = []  # each line of the file is an array element
17with open('record.csv', 'r') as record_read:
18    reader = csv.reader(record_read)
19    for i, each_arr in enumerate(reader):
20        two_dim_arr.append([eval(each) for each in each_arr])
21        
22# printing the arrays in lines
23for each_line in two_dim_arr:
24  print(each_line)