Getting started¶

Welcome!¶

This is an informal course for complete beginners. Our aim will be to build confidence in programming, using the Python programming language and turtle graphics. It’s a training course, so there’s no assessment, and no course credit!

I assume that participants have no programming experience at all. While I will talk through the materials, the course is focused on practical exercises. Questions are always welcome at any time

How to use this course¶

If you get stuck with the exercises, feel free to ask for help from a tutor. You can also help each other‒it would be great if you could introduce yourself to the people at your table and talk about the exercises! Of course, it’s ok to work on your own, if that’s what you prefer.

You can also read ahead and try the next exercise if that helps. If you’ve finished the exercises you can always move on to the next one.

Computer programming and failure¶

Computer programming involves lots of failure‒often you have to fail several times to succeed once, editing the code until it works! This is ok and happens to everyone, even very experienced programmers. As we’ll see later, most of the time there will be an error message, which will give you a clue to the solution for the problem.

What you’ll need¶

You can follow this course using (almost) any copy of Python and something that can edit Python code. That said, there is a Python environment called Thonny which is specially designed for beginners, and that’s what I recommend for this course:

Thonny for Microsoft Windows
Thonny for Mac OS X
Thonny for Linux

Once you’ve installed this start it up. You should see something like this:

_images/thonny.png

If that doesn’t work for you, please first try logging on to Noteable . If that doesn’t work, please try a text editor and Python install .

Throughout the rest of the course, where something differs between Thonny and Noteable, I’ll make this clear with colour-coded boxes. You only need to follow the instructions for the one you’re using!

The instructions for Noteable will sometimes be hidden‒if this is the case just click “Show” to see them.

What is Python, exactly?¶

If you’re doing preparation for the class you can stop reading now! We’ll go through the rest in the class. (Feel free to keep reading if you’re interested, of course â˜ș).

Python is a programming language. You’ve probably heard this term before, but what does it mean? It means that Python takes text that you’ve written (called code), turns it into instructions for your computer, and follows those instructions. We’ll be learning how to write code to do cool and useful stuff. No longer will you be restricted to using other people’s programs to do things with your computer‒you can make your own!

Using Python¶

To start with we’ll use Python as a command-line interpreter (you might also see this referred to as a REPL). This takes text commands and runs them as you enter them, which is very handy for trying things out.

In Thonny just type your commands into the panel titled “Shell” at the bottom of the window.

Click “Show” to see how to do this in Noteable.

Go back to your Noteable home page, click New → Python 3. A new tab will appear looking like this:

_images/notebook.png

Click on the box after In: [ ]. You’ll be able to type your code in there. Unlike in Thonny, you will have to press Shift-Enter to run each line of code.

Interacting With Python¶

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.

Exercise¶

Just above we demonstrated entering a command to figure out some math. Try some maths commands of your own! What operations does python know? Get it to add 239 and 588 together, and then square the result.

Solution¶

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

Running Python files¶

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 run it all at once.

In Thonny: Type your code into the panel at the top of the window:

_images/thonny_code.png

You can then use File → Save As 
. to decide where to save your file.

Click on the green circle with an arrow in it thonny_run to run your program.

In Noteable: You can type multiple lines of code together (using Enter at the end of each line) then press Shift-Enter to run them all together.

Try this for a simple program with more than one line of code, maybe

print("Hello world")
print("something else")

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

Warning

When playing around with turtle in the following sections, 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.