lsystem.js

function l_system (productions, depth, s) {
    if (depth === 0) return s;
    return $.map(s, function (v) { 
        return l_system(productions, depth - 1, productions(v) || [v]); 
    });
}

function run_turtle (turtle, operations, commands) {
    $.each(commands, function (_, c) {
        (operations[c] || $.noop)(turtle);
    });
}

lsystem.py

def l_system(productions, depth, s): 
    if depth == 0: return s
    return (x for c in s for x in l_system(productions, depth-1, productions.get(c, [c]))) 


def run_turtle (turtle, operations, commands):
    return reduce(lambda acc, c: operations.get(c, lambda t:t), turtle, commands)