Simple code to generate a binary .STL file

gen_stl.py

#!/usr/bin/env python3

import sys
import struct
import math

class Vertex:
    def __init__(self, x,y,z):
        self.val = [x,y,z]

    def to_stl(self):
        return struct.pack('fff',self.val[0],self.val[1],self.val[2])
        
class Triangle:
    def __init__(self, v1,v2,v3, n1):
        self.verts = [v1,v2,v3]
        self.norms = n1

    def to_stl(self):
        return self.norms.to_stl() + self.verts[0].to_stl() + self.verts[1].to_stl() + self.verts[2].to_stl() + struct.pack('H', 0)

class STL_File:
    def __init__(self, msg=None):
        self.tris = []
        if msg is None:
            self.header = (80*' ').encode('utf-8')
        else:
            if len(msg)>80:
                self.header=msg[0:80].encode('utf-8')
            else:
                self.header = (msg + (80-len(msg))*' ').encode('utf-8')
    def add_tri(self, tri):
        self.tris.append(tri)

    def to_stl(self):
        rval = self.header
        rval += struct.pack('I', len(self.tris))
        for t in self.tris:
            rval += t.to_stl()
        return rval

def main(args):

    verts = [Vertex(0,0,0),
             Vertex(1,0,0),
             Vertex(0,1,0),
             Vertex(0,0,1),
             ]
    norms = [Vertex(0,0,-1),
             Vertex(0,-1,0),
             Vertex(-1,0,0),
             Vertex(1/math.sqrt(3),1/math.sqrt(3),1/math.sqrt(3)),
             ]

    tris = [Triangle(verts[0],verts[1],verts[2], norms[0]),
            Triangle(verts[0],verts[1],verts[3], norms[1]),
            Triangle(verts[0],verts[2],verts[3], norms[2]),
            Triangle(verts[1],verts[2],verts[3], norms[3]),
            ]
    bob = STL_File()
    bob.add_tri(tris[0])
    bob.add_tri(tris[1])
    bob.add_tri(tris[2])
    bob.add_tri(tris[3])
    with open(args[0], 'wb') as outf:
        outf.write(bob.to_stl())
        # print(bob.to_stl(), file=outf)
    

if __name__=='__main__':
    main(sys.argv[1:])