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I just familarized myself with a Turing machine. I'm in the process of making a semi-accurate virtual Turing machine but I ran into a seemingly simple problem that I just know there is a solution for. I researched online but couldn't find anything that satisfied my issue.

How do I make the variable 'l' callable within the function. It must be callable because if I define the initial value of the variable within the function, when the function loops it will reset the value to 0.

Here is my code: 

blanktape = []
for x in range(1,251):
    x = ' '
    blanktape.append(x)

global l
l = 1
non = ' '
head = blanktape[l]
symbols = [3, 'ee', 'x']

def mconfigb():
    if head == non:
        blanktape[blanktape.index(head)] = 0
        l = l + 2

def mconfigc():
    if head == non:
        blanktape[blanktape.index(head)] = 1
        l = l + 2

def turingmachine():
        while l < len(blanktape) + 1:
            mconfigb()
            mconfigc()
        return blanktape

print turingmachine()
Hackaholic
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01110100
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    I'll parrot comments made in the answers below but I agree with them. First, its a perfect opportunity to use a class. Second, one letter variables tend to be very problematic to work with. Don't be afraid to use longer name like head_location or something like that. – Laurent Bourgault-Roy Mar 20 '13 at 00:20

3 Answers3

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def function(input):
    global globvar
    ....

they have to be declared per-function. but, I think you should wrap all your creation into a turingmachine class and use instance variables.

thkang
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You need to put:

global l

within the function itself (and you may want to rethink your variable naming conventions, l is not a good name).

For example:

xyzzy = 1

def fn():
    global xyzzy
    xyzzy = xyzzy + 1
paxdiablo
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def mconfigb():
     global l

Other functions do this also.

Yarkee
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