Videos
Python for A-Level CS
Pick a topic to watch.
15 video lessons
2:07
Lesson 1
Nested loops
One loop inside another sounds simple, and one sentence about it gets misread every year: for every single pass of the outer loop, the inner loop runs all…
2:02
Lesson 2
Text files
Opening a file takes a mode, and the mode is not a formality. Read gives you what is there. Write throws away what was there and starts a fresh file. Append…
2:06
Lesson 3
Exceptions
Ask Python to turn the word hello into a number and it raises an exception — a value error. And an exception that nobody handles stops the program on the spot…
2:10
Lesson 4
Stacks
A stack is the first abstract data type in this course, and the word abstract is doing real work. What defines a stack is its operations: push, pop, peek…
2:03
Lesson 5
Queues
A queue is the other ADT, and it behaves like a line of people. A new item joins at the back. The next item out leaves from the front. Put the two structures…
2:05
Lesson 6
Linked lists
A linked list is a chain of nodes, and each node holds two things: a piece of data, and a link to the next node. Here a node is just a dictionary with those…
2:14
Lesson 7
Searching
Searching means finding whether a value is in a list, and where. Note the second half of that: what comes back is the position, not the value — the caller…
2:02
Lesson 8
Sorting
Bubble sort only ever looks at neighbours. Walk the list and compare each pair in turn, swapping any that are the wrong way round. Watch the five: compared…
2:11
Lesson 9
Recursion
Recursion is a function that calls itself, and every recursive function has exactly two parts. The base case is the smallest version of the problem, and it is…
2:38
Lesson 10
Classes & objects
A class defines a new kind of thing — a type you invent yourself. This one says a point has an x and a y, and that is all it says: it holds no numbers, because…
2:18
Lesson 11
Inheritance & encapsulation
Inheritance lets a new class start from an existing one instead of from nothing. Animal knows how to describe itself. Now two classes built on it: Bird and…
2:45
Lesson 12
Programming paradigms
A paradigm is a style of organising a program — not a language, a style. The same problem can be written in any of them. Procedural is a list of steps, grouped…
2:40
Lesson 13
Hash tables
A hash table is a list of slots, and the trick is that you never look for anything. You compute where it belongs. Give it the key cat and a function answers…
2:41
Lesson 14
Binary search trees
A binary search tree keeps values sorted by where it puts them. Each node holds a value and links to up to two children, and one rule governs the lot. Take the…
2:12
Lesson 15
Graphs
A graph is a set of nodes joined by edges. The circles are the nodes — you will also see them called vertices — and the lines are edges. That is the whole…