If you haven't yet got python, the latest official installation packages can be found here:

http://python.org/download/

Python 3 is preferable, being the newest version out!

A code editor helps with reading and writing programming code. There are many around, and it is one of the most personal choices a programmer can make - Like a tennis-player choosing their racket, or a chef choosing their favourite knife. To start off with, you'll just want a basic, easy-to-use one that doesn't get in your way, but is still effective at writing python code. Here are some suggestions for those:

• Sublime Text: A great all around editor that's easy to use. It's Ctl+B shortcut lets you run the python file you're working on straight away. Runs on Windows, Mac and Linux.
• Geany: A simple editor that doesn't aim to be too complicated. Available on Windows and Linux (you can probably find it in your package manager).
• TextMate: One of the most famous code editors for Mac, it used to be a paid product but has since been open-sourced.
• Gedit and Kate: if you run Linux using Gnome or KDE respectively, you might already have one of these two installed!
• Komodo Edit: a sleak, free editor for Mac, Windows and Linux, based on the more powerful Komodo IDE.

If you'd like our recommendation, try out Sublime Text first.

Ok, so python is this thing called a programming language. It takes text that you've written (usually referred to as code), turns it into instructions for your computer, and runs those instructions. We'll be learning how to write code to do cool and useful stuff. No longer will you be bound to use others' programs to do things with your computer!

Practically, Python is just another program on your computer. The first thing to learn is how to use and interact with it. There are in fact many ways to do this; the first one to learn is to interact with python's interpreter, using your operating system's (OS) console.

A console (or 'terminal', or 'command prompt') is a textual way to interact with your OS, just as the 'desktop', in conjuction with your mouse, is the graphical way to interact your system.

OS X's standard console is a program called :program:`Terminal`. Open Terminal by navigating to Applications, then Utilities, then double-click the :program:`Terminal` program. You can also easily search for it in the system search tool in the top right.

The command line Terminal is a tool for interacting with your computer. A window will open with a command line prompt message, something like this:

mycomputer:~ myusername$

Different linux distributions (e.g Ubuntu, Fedora, Mint) may have different console programs, usually referred to as a terminal. The exact terminal you start up, and how, can depend on your distribution. On Ubuntu, you will likely want to open :program:`Gnome Terminal`. It should present a prompt like this:

myusername@mycomputer:~$

Window's console is called the Command Prompt, named :program:`cmd`. An easy way to get to it is by using the key combination Windows+R (Windows meaning the windows logo button), which should open a :guilabel:`Run` dialog. Then type :program:`cmd` and hit Enter or click :guilabel:`Ok`. You can also search for it from the start menu. It should look like:

C:\Users\myusername>

Window's Command Prompt is not quite as powerful as its counterparts on Linux and OS X, so you might like to start the Python Interpreter (see just below) directly, or using the IDLE program that Python comes with. You can find these in the Start menu.

The python program that you have installed will by default act as something called an interpreter. An interpreter takes commands and runs them as you enter them - very handy for trying things out.

Just type :program:`python` at your console, hit Enter, and you should enter Python's Interpreter.

To find out which version of python you're running, use python -V to tell you.

After Python opens, it will show you some contextual information similar to this:

Python 3.3.2 (default, May 21 2013, 15:40:45)
[GCC 4.8.0 20130502 (prerelease)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

You can now enter some python code. Try:

print("Hello world")

Press Enter and see what happens. After showing the results, Python will bring you back to the interactive prompt, where you could enter another command:

>>> print("Hello world")
Hello world
>>> (1 + 4) * 2
10

An extremely useful command is help(), which enters a help functionality to explore all the stuff python lets you do, right from the interpreter. Press q to close the help window and return to the Python prompt.

To leave the interactive shell, press Ctrl-Z and then Enter on Windows, or Ctrl-D on OS X or Linux. Alternatively, you could also run the python command exit()!

When you have a lot of python code to run, you will want to save it into a file so, for instance, you can modify small parts of it (fix a bug) and re-run it without having to repeatedly re-type the rest. Instead you can save your code to a file and pass a file name to the :program:`python` executable. It will execute that file instead of launching the interactive interpreter.

Let's try that. Create a file :file:`hello.py` in your current directory with your favorite text editor and write the print command from above. Now save that file. On Linux or OS X, you can also run touch hello.py to create an empty file to edit. To run this file with python, it's pretty easy:

$ python hello.py

On Windows you should also be able to double-click the Python file to run it.

When pressing Enter now, the file is executed and you see the output as before. But this time, after Python finished executing all commands from that file it exits back to the system command prompt, instead of going back to the interactive shell.

And now we are all set and can get started with turtle!

> cd Desktop\Python_Exercises

$ cd Desktop/Python_Exercises