How to make resizable windows with glut?

I am following the sample programs in the OpenGL Superbible, and they make it sound like windows created with glutCreateWindow will be resizable. I am using my own python-version of their Listing 2.2 below, and my windows are never resizable. I am using: PyOpenGL 3.1.7 on macOS Ventura (and "freeglut" (I think it was also the same before I installed freeglut).

Here is the listing:

from OpenGL.GLUT import *
from OpenGL.GL import *
from OpenGL.GLU import *

def change_size(w, h):
    glViewport(0, 0, w, h)
    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()
    aspect_ratio = w/h
    if w <= h:
        glOrtho(-100, 100, -100/aspect_ratio, 100/aspect_ratio, 1, -1)
    else:
        glOrtho(-100*aspect_ratio, 100*aspect_ratio, -100, 100, 1, -1)
    glMatrixMode(GL_MODELVIEW)
    glLoadIdentity()
    
    
def render_scene():
    glClear(GL_COLOR_BUFFER_BIT)
    glColor(1,0,0,0)
    glRectf(-25,25,25,-25)
    glFlush()
        
def setup_rc():
    glClearColor(0, 0, 1, 1)
    
def main():
    glutInit(sys.argv)
    glutInitDisplayMode(GLUT_SINGLE|GLUT_RGBA)
    glutCreateWindow("Simple")
    glutDisplayFunc(render_scene)
    glutReshapeFunc(change_size)
    setup_rc()
    glutMainLoop()
    
main()

is there an easy way to create the main window so it is resizable?

glut is an old library and there are some known issues on various systems, such as a resizing bug on Mac. If you have problems with glut on your system, I recommend you to use glfw which is more recent.

install glfw

pip3 install glfw

There are just a few changes needed to rewrite your code using glfw instead of glut:

from OpenGL.GL import *
from glfw.GLFW import *

def change_size(window, _w, _h):
    w, h = glfwGetFramebufferSize(window)
    glViewport(0, 0, w, h)
    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()
    aspect_ratio = w/h
    if w <= h:
        glOrtho(-100, 100, -100/aspect_ratio, 100/aspect_ratio, 1, -1)
    else:
        glOrtho(-100*aspect_ratio, 100*aspect_ratio, -100, 100, 1, -1)
    glMatrixMode(GL_MODELVIEW)
    glLoadIdentity()
    
def render_scene():
    glClear(GL_COLOR_BUFFER_BIT)
    glColor(1,0,0,0)
    glRectf(-25,25,25,-25)
    glFlush()
        
def setup_rc():
    glClearColor(0, 0, 1, 1)
    
def main():
    if glfwInit() == GLFW_FALSE:
        raise Exception("error: init glfw")

    glfwWindowHint(GLFW_SAMPLES, 8)
    window = glfwCreateWindow(640, 480, "Simple", None, None)
    glfwMakeContextCurrent(window)

    setup_rc()
    glfwSetWindowSizeCallback(window, change_size)  
    change_size(window, 640, 480)
    while not glfwWindowShouldClose(window):
        glfwPollEvents()
        render_scene()
        glfwSwapBuffers(window)
    
main()