Creating a Code Rain Effect with Python and Pygame

Many beginners encounter the pygame package when learning Python because it combines fun visual output with fundamental programming concepts. This article shows how to recreate the iconic "code rain" effect seen in hacker movies using only a small amount of code.

First, import the required modules:

<code>import pygame</code><code>import random</code>

Next, initialize the display and related parameters. Define the screen size, a semi‑transparent black background, and set up pygame, a font, and a surface that will be repeatedly blitted:

<code># parameters
SCREENSIZE = (600, 600)
BLACK = (0, 0, 0, 13)

# initialization
pygame.init()
font = pygame.font.SysFont('宋体', 20)
screen = pygame.display.set_mode(SCREENSIZE)
surface = pygame.Surface(SCREENSIZE, flags=pygame.SRCALPHA)
pygame.Surface.convert(surface)
surface.fill(BLACK)
screen.fill(BLACK)</code>

Prepare the characters that will fall down the screen. The list combines digits (0‑9) and lowercase letters (a‑z), renders each character in green, and creates a column index list for positioning:

<code># content
lib = [chr(i) for i in range(48, 48 + 10)] + [chr(i) for i in range(97, 97 + 26)]  # [0‑9 a‑z]
texts = [font.render(l, True, (0, 255, 0)) for l in lib]
cols = list(range(40))  # each column corresponds to a 15‑pixel step in a 600‑pixel window</code>

The main loop handles quit events, updates the display at a modest frame rate, selects a random character for each column, draws it, and updates the column's vertical position. When a column reaches the bottom or a random chance occurs, it resets to the top:

<code>while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            exit()
    pygame.time.delay(33)
    screen.blit(surface, (0, 0))
    for i in range(n := len(cols)):
        text = random.choice(texts)
        screen.blit(text, (i * 15, cols[i] * 15))
        cols[i] = 0 if cols[i] > 80 or random.random() > 0.95 else cols[i] + 1
    pygame.display.flip()</code>

Putting all parts together yields the complete, runnable script shown below:

<code>import pygame
import random
# parameters
SCREENSIZE = (600, 600)
BLACK = (0, 0, 0, 13)
# initialization
pygame.init()
font = pygame.font.SysFont('宋体', 20)
screen = pygame.display.set_mode(SCREENSIZE)
surface = pygame.Surface(SCREENSIZE, flags=pygame.SRCALPHA)
pygame.Surface.convert(surface)
surface.fill(BLACK)
screen.fill(BLACK)
# content
lib = [chr(i) for i in range(48, 48 + 10)] + [chr(i) for i in range(97, 97 + 26)]  # [0‑9 a‑z]
texts = [font.render(l, True, (0, 255, 0)) for l in lib]
cols = list(range(40))  # font size 15, window 600
while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            exit()
    pygame.time.delay(33)
    screen.blit(surface, (0, 0))
    for i in range(n := len(cols)):
        text = random.choice(texts)
        screen.blit(text, (i * 15, cols[i] * 15))
        cols[i] = 0 if cols[i] > 80 or random.random() > 0.95 else cols[i] + 1
    pygame.display.flip()</code>

Running this script opens a 600×600 window where green alphanumeric characters cascade down the screen, recreating the nostalgic "code rain" visual.