Further information.

What is a context manager

Instead of using the approach shown in How to write to a file it is possible to write to a file using the following:

f = open("squares.csv", "w")
for n in range(1, 101):
    f.write(f"{n}, {n ** 2}\n")
f.close()

However, when doing so it is important to close the file. Without this the file remains inaccessible for other purposes.

Thus, it is preferred to use:

with open("squares.csv", "w") as f:
    for n in range(1, 101):
        f.write(f"{n}, {n ** 2}\n")

In this case, the indented block after with open("squares.csv", "w") as f: is the context within which the file f is open. It will be closed outside of that indented block.

This is an example of a context manager. There are other examples of this in Python such as try and except loops.

Working with files with numpy

It is possible to write a numpy array to a file using the savetxt function. For example:

import numpy as np

A = np.array(
    (
        (1, 5, 3),
        (8, 1, 2),
        (3, 5, 1),
    )
)
np.savetxt("array.txt", A)

It is possible read a file in to a numpy array using the loadtxt function:

A = np.loadtxt("array.txt")
A

array([[1., 5., 3.],
       [8., 1., 2.],
       [3., 5., 1.]])

Working with files with pathlib

The pathlib library is a powerful tool for reading, writing and manipulating files.

The documentation for pathlib is available here: docs.python.org/3/library/pathlib.html