Variables are how you can store values in the computer's memory to work with in your Python code. A variable is given a name and a value. You can then use the variable by referencing its name, and change the value if needed (hence it is 'variable', or can vary).

Variables have different data types, depending on what kind of information they store. This allows the computer to know what kind of actions can be done with that information, for example whether or not you can do arithmetic with it.

To create a variable in Python, you just need to give it a name by typing one, then use an equals sign (=) to assign it a value. Variable names in Python can only start with either a letter or an underscore and they cannot include any spaces. For more information on what you can include when naming a variable, see w3school's guidance on Python variable names.

There are many different data types in Python, but here are some useful ones to start with:

• Strings - Some characters, such as letters, symbols, or numbers, which are treated as 'text'. They must be surrounded by either single or double quote marks.
• Integers - Positive or negative whole numbers.
• Floats - Floating point numbers, shortened to float, are decimal numbers, either positive or negative.
• Booleans - The Boolean data type is data that is either True or False (it can be shortened to bool).
• Lists - Lists allow you to put multiple values together in one variable, separated by commas, so you can access them as a group or individually.

As mentioned above, lists in Python are a way of storing multiple separate values in one variable. This means you can work with the whole collection as well as individual items by accessing them using an index number or position in the list.

Lists are stored in a particular order, which can have duplicate values, and to which you can add, remove, and reorder values. Lists must be written in square brackets, with each value separated by a comma. Items in a list can be different data types, like strings, numbers, or even another list!

Python list indexes start from 0, so to access the first item in the list with the name my_list you would use my_list[0], to access the second item you'd use my_list[1], etc.

For more on lists, see w3schools' pages on Python lists.

Operators are the Python commands you use to do things with values, whether or not they are stored in a variable. They are mostly represented by punctuation characters, though some of their meanings might not be what you'd expect.

• Assignment operators are used to assign values to variables. The equals sign = is most common, as it is used to assign a value to a variable, either when creating it or when changing the value. You might also use =+ to increment a variable's value by 1 and assign it that new value.
• Arithmetic operators are used to do mathematical calculations, like +, -, *, and /.
• Comparison operators are used to compare values, e.g. when making decisions. So you might use == to compare if two values are equal, != to compare if values aren't equal, or the greater or less than symbols for checking which value is greater.
• Logical operators are used to combine statements when making decisions in code, using keywords like and, or, and not.

Comments are crucial in any coding langauge as a way of explaining to yourself and others what your code is doing, adding important notes, and translating your pseudocode notes into actual code.

In Python, you tell the computer to ignore a line (or the rest of a line) by using a hash # symbol. Once the computer reaches a # it will know the rest of the line is a comment, not code to be executed, and will skip ahead to the next line.

Use comments to note what parts of your code do or to add information that you or someone else might find useful in the future. Comments are also a way of stopping a line or lines of code running whilst you test or try and troubleshoot it. Adding a # to the start of a line of code will mean it will not run.

Loops are used in Python to repeat code multiple times, either for a particular set of values or while a statement remains true. So this might be for a particular list of values (like some names) or until a changing numerical variable is above or below a certain value.

This means there are two kinds of loops, for loops and while loops, and we're emphasising those words because they are how you create these loops.

The for keyword in Python is how you start a for loop. If you're going to loop through a Python list, you then create a variable that stands for the individual values in that list, then use the keyword in, then finish with the name of the list in question, and a colon. So you'll end up with something like:

for item in shopping_list

where shopping_list is a list variable you've already created.

The while keyword creates a while loop, which means that instead of running through values in turn, the loop returns to evaluate a condition each time the code runs, to check whether it should still be running. This makes while loops useful if you don't know when the loop will need to stop, but want the code to make that decision based on the condition you give. A while loop is created by starting with while, then defining a condition to be tested each time, and ending the line with a colon.

Note: In Python, all the code inside the loop (after the colon) must be indented, as this tells the computer which code is in the loop. Once the indentation ends, that is the end of the loop.

To see more about these loops and have a go, see the Loops section of the Getting started with coding in Python workbook.

As well as automating repetition, Python can be useful for also automating whether or not certain code should run. By giving the computer a statement to evaluate, you can make it decide whether or not the subsequent code should run, using an if condition. The statement can be evaluated to either True or False, and a True statement will make the code run.

There are multiple levels you can have to an if condition. On the most basic level, you can just give one option, to run some code if the statement is True, or skip past the code without an alternative if it is False. Or you can offer an else as well: code that runs if the statement was False. You can also add extra statements that could be true into your condition using elif, short for 'else if'.

Like a loop, you start an if condition with a keyword, in this case the if keyword. You then write your condition to be evaluated, within brackets, and then end the line with a colon. As with loops, any code that should happen if the code is True needs to be indented, to show the computer which code is inside the condition. A simple if condition might look like:

if (day == 'Friday'):
    print('Yay it is Friday')
else:
    print('Sadly it is not Friday')

For more examples of if conditions, see the if conditions section of the Python workbook.