BeginnerCoder
Donate← Data Structures
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Lesson 1 — Stack
Stack: last in, first out
A data structure is a way of organising data so certain operations are fast. A stack works like a pile of plates: you only add to the top (push) and only take from the top (pop). The last thing in is the first thing out — LIFO. A Python list is a perfect stack: append() pushes, pop() removes and returns the last item.
stack = [1, 2]
stack.append(3) # [1, 2, 3]
stack.pop() # returns 3, stack is [1, 2]
Why it matters: the Undo button in every editor is a stack of your recent actions.
Want it another way?
Task
Push the three actions onto history, then undo (pop) the last one. Expected: undo type "!" and history with two actions.
Run your code — when the output matches the task, you will see a green check. Then mark the lesson complete.
Test your knowledge
Test your knowledgeA quick 3-question quiz on this lesson — instant feedback.