Writing multiple NumPy arrays (the ndarray objects) into a file

Overview:

The savez() and savez_compressed() functions of the Python NumPy module write multiple ndarray objects into a disk file.
While savez() writes the ndarray objects in uncompressed form, the savez_compressed() writes the arrays in compressed form.
For both savez() and savez_compressed(), when no file name extension is given .npz is assumed as the extension of the file.
Unlike savez() and savez_compressed() functions the save() function writes only one ndarray per disk file.

# Example Python program that uses numpy.savez()
# function to save multiple arrays into a file.
import numpy as np

# Create a two-dimensional array
a1 = np.ones((2, 2), dtype = np.int8)

for x in range (0, 1):
for y in range (0, 1):
a1[x][y] = x * y

# Create a three-dimensional array
a2 = np.ones((3, 3, 3), dtype = np.int8)

for x in range (0, 3):
   for y in range (0, 3):
       for z in range (0, 3):
           a2[x][y][z] = x * y * z

# Write both the arrays into a .npz file - Uncompressed form
np.savez("multi_array_uncompressed.npz", array1 = a1, array2 = a2)

# Write both the arrays into a .npz file - Compressed form
np.savez_compressed("multi_array_compressed.npz", array1 = a1, array2 = a2)

The compressed version saves the overhead of 129 bytes when compared to the uncompressed version.

-rw-r--r-- 1 root u1 412 Aug 22 14:29 multi_array_compressed.npz

-rw-r--r-- 1 root u1 541 Aug 22 14:29 multi_array_uncompressed.npz

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The file is opened using the vi editor.

sudo vi multi_array_compressed.npz

The savez_compressed() function writes everything in compressed form including the header information.

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