Touring Turing

1 Alan Turing

In 1936, a few years before the outbreak of World War II, Alan Turing invented the Turing Machine.
This was a hypothetical device (not one to be actually built) that could read and change symbols on an infinitely long tape, according to a table of rules.
With this simple idea, Computer Science was born, as the Turing Machine was theoretically capable of performing any calculation that was computable.
It took a few more years before actual computers were constructed, but even today we can talk about computers and programming languages in terms of their Turing completeness. This means that they are able to do exactly what a Turing Machine can do.

For this project, we'll be using the Python 3 Programming language.
You've used Scratch before, which is a Graphical Programming Language. Python does the same sort of thing, but you program using text instead of blocks.
If you're working on this outside of school, you can download it from the following links.
Python 3.7.3 for Mac
Python 3.7.3 for Windows
If you need Python 3 for Linux - use your package manager sudo apt-get update && sudo apt-get install python3 idle3 (on Ubuntu for instance)
If you're working in school, then you should find a program called Thonny, inside the computing folder on the desktop.

Open up Thonny. You should be presented with a screen that looks a little like this:

Thonny is an Integrated Development Environment (IDE) for Python, particularly suitable for beginners. You can create, edit and run Python files using it.
We can write code in the code editor window (the upper window), and when you press the green button with a white triangle in it, it gets executed and the results will be shown in the shell (the lower window).
You can also input code one line at a time in the shell prompt. When you hit enter, that line of code gets executed right away.

One of Turing's key ideas was an infinitely long tape, upon which symbols could be added, read and changed.
In modern computers this tape is called RAM, and is made up of very complex circuits.
Just like in a Turning machine though, we can add data to RAM, read data from RAM and change data in RAM.

myName = 'Alice'

You can obviously use your own name.
You have now stored your name in RAM. You have done this using a variable
For now think of a variable is being made up of an identifier (myName) and a value (Alice)
Note - Once you have hit ENTER you can not delete what has been executed, any more than you can unbreak an egg. If you make a mistake, just type it out again (or the upper arrow key on your keyboard to bring up the last command again, and alter it from there).

Turing's original idea called for an infinitely long tape, that we could store an infinite amount of information on.
RAM is pretty big, even if it's not infinite. A typical Computer might have anywhere between 2Gb and 16Gb or RAM.
This would be enough space to store between 1000000000 and 4000000000 characters, which is enough for us.
Try creating some variables for your friend's names. Each one must have it's own unique identifier though

firstFriendName = 'Robert'
secondFriendName = 'Charles'
thirdFriendName = 'David'
fourthFriendName = 'Eve'

5thFriendName = 'Faith'

You'll get back a message saying you've used invalid syntax.
This is known as a syntax error. It means you haven't conformed to the rules of the language.
Here are the rules for Python's Variable Identifiers:
1. Must not start with a number.
2. Must not contain symbols like !, @, #, $, % etc.
3. Must not contain spaces (use _ instead)
4. Are case sensitive (myname, myName, MyName and MYNAME would all be different variable identifiers.)
There's also a few reserved words you should avoid for identifiers, like not and continue, but you'll learn these as you go along.

Now we have some variables stored, we'd best learn how to read them, as that was one of the stipulations of the Turing machine's tape.
You can read the value of a variable just by writing it's name.

myName
secondFriendName

firstFriendName = 'Bob'
secondFriendName = 'Charlie'
thirdFriendName = 'Dave'

mum = 'Alice'
dad = 'Bob'
cat = 'Eve'

foo = 10
bar = 3.142
baz = 'Hello World!'
qux = True

Now, for each of the variables, you can find out it's type using the type() inbuilt function.

type(foo)

<class 'int'>

This would tell me that the data-type was an int, which is short for integer.
Look up each of the data-types for the variables above and then use the web to find out what they each mean (in simple English).

6 + 4

In Python we can use + and - for addition and subtraction, / and * for division and multiplication.
There are lots of mathematical operators we can use. Here is a table of all of them for reference later on.
In the examples below a = 10 and b = 20

Operator	Description	Example
`+`	Addition - Adds values on either side of the operator	a + b will give 30
`-`	Subtraction	b - a will give 10
`*`	Multiplication	a * b will give 200
`/`	Division	b / a will give 2
`%`	Modulus - remainder of a division	b % a will give 0
`**`	To the power of	a**b will give 10 to the power 20
`//`	Division and round down	9//2 is equal to 4 and 9.0//2.0 is equal to 4.0

(24+1)*4