🧠 Core Python Skills

This knowledge organiser summarises the Python programming skills you have practised in this lesson.

• Inputs and outputs – how programs communicate with users
• Variables and data types – how data is stored and used
• Selection (if / elif / else) – how programs make decisions
• Iteration (while loops and for loops) – how programs repeat code
• 1D and 2D lists – how programs store multiple pieces of data

You should be able to read, write, and explain programs that use these skills.

⌨️ Inputs, Outputs and Variables

What is a variable?

• A variable is a named storage location in memory
• It stores data so it can be reused later
• The value can change while the program runs

Inputs and outputs

• input() pauses the program and waits for the user
• The value entered is always stored as a string
• print() displays information to the user

name = input("Enter your name: ")
print(f"Hello {name}")

Why this works: The input is stored in a variable and reused in the output.

🔢 Casting Data Types

Why casting is needed

• All input from input() is stored as text
• Text cannot be used for calculations
• Casting converts data into a different type

Common data types

• str – text
• int – whole numbers
• float – decimal numbers

num = int(input("Enter a number: "))
print(num * 2)

Exam reminder: Without int(), Python treats numbers as text.

🔀 Selection (IF / ELIF / ELSE)

What is selection?

• Selection allows programs to make decisions
• Conditions are checked from top to bottom
• Only one branch will run

How it works

• if checks the first condition
• elif checks additional conditions
• else runs if none are true

colour = input("Enter a colour: ")

if colour.lower() == "red":
    print("Correct")
elif colour.lower() == "blue":
    print("Correct")
else:
    print("Incorrect")

Why .lower() matters: It avoids errors caused by capital letters.

🔁 While Loops

What is a while loop?

• A while loop repeats while a condition is true
• The condition is checked before each loop

When to use it

• When you do not know how many times the loop will run
• When waiting for correct user input

password = input("Enter password: ")

while password != "Secret123":
    print("Incorrect")
    password = input("Try again: ")

print("Password accepted")

Important rule: The variable used in the condition must be updated.

🔂 while True Loops

What does while True mean?

• The loop condition is always true
• The loop will never stop on its own

How does it stop?

• break is used to exit the loop
• The loop stops when break runs

while True:
    guess = input("Enter a colour: ")
    if guess.lower() == "red":
        print("Correct")
        break
    else:
        print("Incorrect")

Exam tip: Always explain where and why the loop ends.

🔢 For Loops

What is a for loop?

• A for loop repeats code a fixed number of times
• A loop variable tracks each repetition

Understanding range()

• range(start, end)
• The start value is included
• The end value is not included

for i in range(1, 13):
    print(f"{i} x 8 = {i * 8}")

Common error: Expecting the loop to include the final value.

📋 1D Lists

What is a list?

• A list stores multiple values in one variable
• Each value has an index number

Indexing

• The first item is at index 0
• The second item is at index 1

sports = ["Shotput", "Javelin", "Diving"]

for i in range(0, 3):
    print(sports[i])

Exam tip: Index values always start at 0.

🧮 2D Lists

What is a 2D list?

• A list containing other lists
• Often used to store records

Accessing values

• First index selects the record
• Second index selects the value within the record

landmarks = [
    ["Eiffel Tower", "Paris"],
    ["Big Ben", "London"],
    ["Sagrada Familia", "Barcelona"]
]

print(landmarks[0][0])
print(landmarks[0][1])

Outputs:

Eiffel Tower
Paris

Searching a 2D list

for i in range(0, len(landmarks)):
    if landmarks[i][1] == "Paris":
        print(landmarks[i][0])

Outputs:

Eiffel Tower