If you haven’t yet got python, the latest official installation packages can be found here:
Python 3 is preferable, being the newest version out!
Note
On Windows, you’ll want to add Python to your PATH, so it
can be found by other programs. With Python 3.5 or later, there should be
and option to do this in the installer. Otherwise, you can navigate to your
installation directory (C:\Python34\), open the Tools,
then Scripts folder, and run the win_add2path.py
file by double clicking on it.
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:
If you’d like our recommendation, try out Sublime Text first.
Tip
Wordpad, TextEdit, Notepad, and Word are not suitable code editors.
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 - you can make your own!
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 conjunction with your mouse, is the graphical way to interact your system.
OS X’s standard console is a program called Terminal. Open Terminal by navigating to Applications, then Utilities, then double-click the 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 Gnome Terminal. It should present a prompt like this:
myusername@mycomputer:~$
Window’s console is called the Command Prompt, named 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
Run dialog. Then type cmd and hit Enter or
click 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 text commands and runs them as you enter them - very handy for trying things out.
Just type python at your console, hit Enter, and you should
enter Python’s Interpreter.
To find out which version of python you’re running,
instead type python -V in your console to tell you.
After Python opens, it will show you some contextual information similar to this:
Python 3.5.0 (default, Sep 20 2015, 11:28:25)
[GCC 5.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>
Note
The prompt >>> on the last line indicates that you are now in an interactive Python interpeter session, also called the “Python shell”. This is different from the normal terminal command prompt!
You can now enter some code for python to run. 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 and go back to the console (the system 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()!
Just above we demonstrated entering a command to figure out some math. Try some math commands of your own! What operations does python know? Get it to tell you what 239 and 588 added together, and then squared is.
Here are some ways you might have got the answer:
>>> 239 + 588
827
>>> 827 * 827
683929
>>> (239 + 588) * (239 + 588)
683929
>>> (239 + 588) ** 2
683929
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 the code without having to repeatedly re-type the rest. Instead of typing commands in one-by-one you can save your code to a file and pass the file name to the python program. It will execute that file’s code instead of launching its interactive interpreter.
Let’s try that! Create a file hello.py in your current directory
with your favorite code 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
Note
Make sure you are at your system command prompt, which will have $ or
> at the end, not at python’s (which has >>> instead)!
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!
Note
Not getting “Hello world” but some crazy error about “can’t open file” or “No such file or directory?” Your command line might not be running in the directory that you saved the file in. You can change the working directory of your current command line with the cd command, which stands for “change directory”. On Windows, you might want something like:
> cd Desktop\Python_Exercises
On Linux or OS X, you might want something like:
$ cd Desktop/Python_Exercises
This changes to the directory Python_Exercises under the Desktop folder (yours might be somewhere different). If you don’t know the location of the directory where you saved the file, you can simply drag the directory to the command line window. If you don’t know which directory your shell is currently running in use pwd, which stands for “print working directory”.
Warning
When playing around with turtle, avoid naming your file turtle.py
— rather use more appropriate names such as square.py or
rectangle.py. Otherwise, whenever you refer to turtle, Python
will pick up your file instead of the standard Python turtle module.