hellocircle.py

# Import everything in the p5.py library
from p5 import *

def draw():
    # On each frame...
    if mouse_is_pressed:
        fill(100) # Fill color gray
    else:
        fill(255) # Fill color white
    
    # Draw a circle of radius 100
    # at the position of the mouse
    circle((mouse_x, mouse_y), 100)
# ---

# Run the sketch
run()