GCSE Computer Science Theory

Data Structures

A data structure is a specialized format for organizing and storing data.

Arrays vs. Lists

It is essential that you know the difference between an array and a list.

A list can contain a mixture of data types, including other data structures.
An array must contain all the same data types (i.e. only integers or only strings). These are usually more efficient than a list.

Data structure operations in Python

Data Structure	Example Values	Valid Operations	Example of Operation
One-Dimensional array	`a = array([1, 2, 3])`	indexing	`a[0] = 1`
One-Dimensional list	`a = [1, True, 'a']`	indexing	`a[0] = 1`
	–>	appending	`a.append(456.1)`
	–>	length	`len(a)`
Two-Dimensional array	`a = array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])`	indexing	`a[0] = 1`
Two-Dimensional list	`a = [[1, '2', '3'], [4, 5, '6'], ['7', 8, '9']]`	indexing	`a[0] = 1`
	–>	appending	`a.append([10, 11, 12])`
	–>	length	`len(a)`
Dictionary	`a = {'key': 'value'}`	indexing	`a['other key] = 'new value`
String	`a = 'string'`	length	`len(a)`
	–>	position	`a[2]`
	–>	substring	`a[1:5]`]
	–>	concatenation	`a + ' string`
	–>	String to Integer	`int('345')`
	–>	String to Float	`float('123.45')`
	–>	Integer to String	`str(345)`
	–>	Float to String	`str(123.45)`

Classes in Python

A class is a quasi-template for creating objects. Consider this example:

class Human():
    def __init__(self, name, age):
        self.name = name
        self.age = age
    
    def have_birthday(self):
        self.age += 1

my_human = Human('Jacob', 4)

This is a template for creating a human. We can use this Human template in order to create instances of the human with their own properties (so they can have their own names and ages). For the exam you do not need to understand the four main OOP class concepts (inheritance, etc.), neither do you need to know the syntax for defining, altering and creating an instance of a class, but you do need to know about classes as a data structure (even though technically classes are programming paradigms and not data structures)