Can someone explain to me this Turing machine code?
Question: I am newbie to Python so I don't really understand this. It's some kind of
Turing machine that should write binary number, but I can't figure out what's
going on after these rules

    
    
    from collections import defaultdict
    import operator
    
    # Binary counter
    # (Current state, Current symbol) : (New State, New Symbol, Move)
    rules = {
        (0, 1): (0, 1, 1),
        (0, 0): (0, 0, 1),
        (0, None): (1, None, -1),
        (1, 0): (0, 1, 1),
        (1, 1): (1, 0, -1),
        (1, None): (0, 1, 1),
    }
    # from here I don't really understand what's going on
    
    def tick(state=0, tape=defaultdict(lambda: None), position=0):
        state, tape[position], move = rules[(state, tape[position])]
        return state, tape, position + move
    
    system = ()
    for i in range(255):
        system = tick(*system)
        if(system[2] == 0):
            print(map(operator.itemgetter(1), sorted(system[1].items())))
    


Answer: It is a state machine. At each tick a new state is computed based on the old
state and the contents of tape at 'tape position' in this line:

    
    
    state, tape[position], move = rules[(state, tape[position])]
    

This statement is a destructuring assignment. The righthand side of the
assignment will give you an entry of rules, which is a tuple of three
elements. These three elements will be assigend to state, tape [position] and
move respectively.

Another thing that might puzzle you is the line:

    
    
    system = tick(*system)
    

especially the *.

In this line the (processor clock) tick function is called with the contents
of tuple 'system' unpacked into separate parameters.

I hope this is clear enough, but the fact that you're interested in a Turing
machine tells me that you've got something with computer programming... ;)

