Saving arrays in Python

npy for one array, npz for several, savetxt when a human must read it.

import numpy as np

grid = np.arange(6).reshape(2, 3)
labels = np.array(["a", "b"])

np.save("grid.npy", grid)
np.savez("bundle.npz", grid=grid, labels=labels)
np.savetxt("grid.csv", grid, fmt="%d", delimiter=",")

print(np.load("grid.npy"))
with np.load("bundle.npz") as bundle:
    print(sorted(bundle.files), bundle["labels"])
print(np.loadtxt("grid.csv", delimiter=",", dtype=int))

How it works

save writes a single array with its dtype and shape.
savez bundles named arrays into one archive.
loadtxt and savetxt trade speed for legibility.

Keywords and builtins used here

as
int
print
sorted
with

The run, in numbers

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Step 2 of 2 in Randomness & storage, step 21 of 22 in NumPy.

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