medium_ray_tracing_code_1.py

import numpy as np
import matplotlib.pyplot as plt

width = 300
height = 200

camera = np.array([0, 0, 1])
ratio = float(width) / height
screen = (-1, 1 / ratio, 1, -1 / ratio) # left, top, right, bottom

image = np.zeros((height, width, 3))
for i, y in enumerate(np.linspace(screen[1], screen[3], height)):
    for j, x in enumerate(np.linspace(screen[0], screen[2], width)):
        # image[i, j] = ...
        print("progress: %d/%d" % (i + 1, height))

plt.imsave('image.png', image)

the png is black

Well, nothing is written in the image. It's part of an article:
https://medium.com/swlh/ray-tracing-from-scratch-in-python-41670e6a96f9?sk=4edf81600f5c0941aa58907bbfb2151d