Code Examples

print("Hello, World!")          # Prints the text between the quotes
print("My name is Alice")         # You can print anything you like
print(42)                         # Numbers don't need quotes
print(3.14)                       # Decimals work too
print("Sum:", 5 + 3)             # Comma separates items — prints: Sum: 8
print()                            # Empty print() = blank line

name = input("What is your name? ")   # Stores whatever the user types
print("Hello,", name)              # Uses the stored value

# ⚠️ input() always returns a STRING. To do maths, convert it first:
age_text = input("Enter your age: ")   # "14" — still a string!
age = int(age_text)                    # Now it's the integer 14
print("Next year you will be", age + 1)  # Works! Output: Next year you will be 15

# Shortcut — convert immediately on one line:
score = int(input("Enter score: "))     # Gets input AND converts in one step
height = float(input("Enter height (m): "))# Use float() for decimals

# The four main data types:
name       = "Alice"      # str  — text in quotes (single or double)
age        = 13           # int  — whole number, no decimal
height     = 1.65        # float — decimal (floating point) number
is_student = True        # bool — only True or False (capital T/F!)

# Checking the type
print(type(name))         # <class 'str'>
print(type(age))          # <class 'int'>

# Variables can change value
age = 14                   # Reassign — age is now 14
age = age + 1             # Use old value to make new value — now 15
age += 1                   # Shorthand for age = age + 1 — now 16

# Type conversion
score_str = "87"          # This is a string
score_int = int(score_str)# Convert to integer: 87
score_flt = float(score_str)# Convert to float: 87.0
back_str  = str(87)        # Integer to string: "87"

# ARITHMETIC OPERATORS
print(10 + 3)       # 13  — addition
print(10 - 3)       # 7   — subtraction
print(10 * 3)       # 30  — multiplication
print(10 / 3)       # 3.333... — division (always gives float)
print(10 // 3)      # 3   — integer division (whole number only)
print(10 % 3)       # 1   — modulus (the remainder after dividing)
print(2 ** 8)       # 256 — exponent (2 to the power of 8)

# BIDMAS — order matters!
print(2 + 3 * 4)    # 14  — multiplication FIRST, then add
print((2 + 3) * 4)  # 20  — brackets override BIDMAS

# COMPARISON OPERATORS (return True or False)
print(5 == 5)        # True  — equal to (note: == not =)
print(5 != 3)        # True  — not equal to
print(10 > 7)        # True  — greater than
print(3 >= 3)        # True  — greater than or equal to
print(4 < 2)         # False — less than

# LOGICAL OPERATORS
print(True and False)  # False — BOTH must be True
print(True or False)   # True  — at least ONE must be True
print(not True)        # False — reverses the boolean

# Useful built-in maths functions
print(abs(-15))       # 15  — absolute value (removes minus sign)
print(round(3.756, 2))# 3.76 — round to 2 decimal places
print(max(4, 9, 2))   # 9   — largest of the given values
print(min(4, 9, 2))   # 2   — smallest value

word = "Computing"

# Length
print(len(word))           # 9 — number of characters

# Indexing — position starts at 0
print(word[0])             # C — first character
print(word[4])             # u — 5th character (index 4)
print(word[-1])            # g — last character
print(word[-3])            # i — 3rd from end

# Slicing — word[start:stop] (stop is NOT included)
print(word[0:4])           # Comp — characters 0,1,2,3
print(word[4:])            # uting — from index 4 to end
print(word[:7])            # Computi — from start up to index 7

# String methods (they don't change the original — they return new strings)
print(word.upper())        # COMPUTING
print(word.lower())        # computing
print(word.replace("ing", "er")) # Computer
print(word.count("i"))     # 1 — how many times "i" appears
print("comp" in word)     # False — case-sensitive!
print("Comp" in word)     # True

# Concatenation (joining strings)
first = "Hello"
last  = "World"
print(first + " " + last)  # Hello World

# f-strings — the modern, clean way to embed variables in text
name  = "Bob"
score = 87
print(f"Student {name} scored {score}%")        # Student Bob scored 87%
print(f"Grade: {score/100:.1%}")                   # Grade: 87.0%
print(f"Pi is approximately {3.14159:.2f}")         # Pi is approximately 3.14

# Basic if / else
temperature = 22

if temperature >= 25:            # Condition to test
    print("It's hot — wear sunscreen!") # Runs if condition is True
else:                              # Runs if condition is False
    print("Not too hot today.")

# Multiple conditions with elif (else-if)
score = int(input("Enter score: "))

if score >= 90:
    grade = "A*"                   # 90 or above
elif score >= 80:
    grade = "A"                    # 80–89
elif score >= 70:
    grade = "B"                    # 70–79
elif score >= 60:
    grade = "C"                    # 60–69
elif score >= 50:
    grade = "D"                    # 50–59
else:
    grade = "U"                    # Below 50

print(f"Grade: {grade}")

# AND / OR in conditions
age        = 15
has_ticket = True

if age >= 12 and has_ticket:     # BOTH must be True
    print("Welcome to the show!")
else:
    print("Sorry, you cannot enter.")

# Nested if (an if inside an if)
weather = "sunny"
if weather == "sunny":
    if temperature > 20:
        print("Perfect beach day!")
    else:
        print("Sunny but chilly.")
else:
    print("Stay inside.")

# range(stop) — 0 up to (but not including) stop
for i in range(5):
    print("Count:", i)               # 0, 1, 2, 3, 4

# range(start, stop) — start up to (not including) stop
for i in range(1, 11):             # 1 to 10
    print(i, "x 3 =", i * 3)

# range(start, stop, step)
for i in range(0, 21, 2):          # Even numbers: 0, 2, 4, ... 20
    print(i, end=" ")                # end=" " keeps on same line

# Looping over a list
subjects = ["Maths", "English", "Computing", "Science"]
for subject in subjects:
    print(f"I study {subject}")

# Looping over a string (character by character)
for letter in "Python":
    print(letter, end="-")          # P-y-t-h-o-n-

# Accumulator pattern — total in a loop
total = 0                           # Start at 0 BEFORE the loop
for n in range(1, 101):           # 1 to 100
    total += n                      # Add each number to total
print("Sum 1–100:", total)        # 5050

# Basic while loop
count = 1                          # Initialise before the loop
while count <= 5:                  # Condition checked EACH iteration
    print("Count:", count)
    count += 1                     # MUST update — or infinite loop!

# Input validation — keep asking until valid
age = int(input("Enter age (5–120): "))
while age < 5 or age > 120:       # Reject invalid values
    print("Invalid — must be 5 to 120")
    age = int(input("Try again: "))
print("Valid age:", age)

# While True loop with break — runs forever until break
while True:
    answer = input("Type 'quit' to exit: ")
    if answer.lower() == "quit":
        print("Goodbye!")
        break                       # Exits the loop immediately
    print(f"You typed: {answer}")

# Creating lists
scores  = [85, 92, 78, 65, 99]    # List of integers
names   = ["Alice", "Bob", "Cara"] # List of strings
empty   = []                         # Empty list (start adding later)

# Accessing elements — index starts at 0
print(scores[0])       # 85  — first element
print(scores[2])       # 78  — third element
print(scores[-1])      # 99  — last element
print(scores[1:4])    # [92, 78, 65] — slice

# Modifying lists
scores[0] = 90         # Change first element to 90
scores.append(75)     # Add 75 to the END
scores.insert(2, 50)  # Insert 50 at position 2 (pushes others right)
scores.remove(65)     # Remove first occurrence of 65
removed = scores.pop()# Remove AND return the last element

# Useful list operations
print(len(scores))    # Number of elements in the list
print(sum(scores))    # Total of all numbers
print(max(scores))    # Highest value
print(min(scores))    # Lowest value
print(scores.index(78)) # Find position of value 78
print(78 in scores)   # True if 78 is in the list

# Sorting
scores.sort()          # Sort ascending (modifies original)
scores.sort(reverse=True) # Sort descending
sorted_copy = sorted(scores) # Returns new sorted list, keeps original

# 2D list (list of lists — like a table)
grid = [[1,2,3],
         [4,5,6],
         [7,8,9]]
print(grid[1][2])     # 6 — row 1 (middle), column 2 (rightmost)

# Procedure — does a task, no return value
def greet(name):                   # 'name' is the parameter
    print(f"Hello, {name}!")        # Uses the parameter

greet("Alice")                      # "Alice" is the argument — prints: Hello, Alice!
greet("Bob")                        # Re-use with different argument

# Function — returns a value
def calculate_area(length, width): # Two parameters
    area = length * width          # Local variable — only exists here
    return area                     # Sends result back to caller

room  = calculate_area(5, 3)      # Call with arguments 5 and 3
field = calculate_area(100, 50)   # Reuse function easily
print(f"Room: {room} m²")          # 15

# Default parameter values
def power(base, exponent=2):       # exponent defaults to 2 if not given
    return base ** exponent

print(power(5))                    # 25   — uses default exponent=2
print(power(2, 10))               # 1024 — overrides default

# Global vs Local scope
total = 0                          # GLOBAL — accessible everywhere

def add_to_total(amount):
    global total                   # Declare we want to use/modify the global
    temp = amount * 2             # LOCAL — only exists inside this function
    total += amount

add_to_total(10)
add_to_total(5)
print(total)                       # 15

# Returning multiple values
def min_max(data):
    return min(data), max(data)   # Returns a tuple of two values

lo, hi = min_max([4, 9, 2, 7])  # Unpack into two variables
print(f"Min={lo}, Max={hi}")       # Min=2, Max=9

def linear_search(data, target):
    """Search through data list for target value.
       Returns index if found, -1 if not found."""
    for i in range(len(data)):     # i goes from 0 to last index
        if data[i] == target:      # Check each element
            return i               # Found! Return its index
    return -1                      # Not found — return -1 by convention

# Testing the function
numbers = [34, 7, 23, 32, 5, 62]
result  = linear_search(numbers, 32)

if result != -1:
    print(f"Found 32 at index {result}")  # Found 32 at index 3
else:
    print("32 not found in the list")

# Works for strings too
names = ["Alice", "Bob", "Charlie", "Diana"]
print(linear_search(names, "Charlie"))  # 2
print(linear_search(names, "Eve"))      # -1 (not found)

def bubble_sort(data):
    """Sort a list in ascending order using bubble sort."""
    n = len(data)                      # Total number of items

    for pass_num in range(n - 1):      # n-1 passes maximum
        swapped = False               # Track if any swap happened this pass

        for i in range(0, n - pass_num - 1): # Don't check already-sorted end
            if data[i] > data[i + 1]:  # Left item bigger than right?
                # Swap them — Python's elegant swap:
                data[i], data[i+1] = data[i+1], data[i]
                swapped = True        # Record that a swap happened

        if not swapped:              # If NO swaps, list is already sorted
            break                      # Optimisation — stop early!

    return data

# Demonstration with trace
nums = [64, 25, 12, 22, 11]
print("Before:", nums)               # [64, 25, 12, 22, 11]
bubble_sort(nums)
print("After: ", nums)               # [11, 12, 22, 25, 64]

# TRACE TABLE (mental model):
# Pass 1: [25,12,22,11,64] — 64 bubbles to end
# Pass 2: [12,22,11,25,64] — 25 moves right
# Pass 3: [12,11,22,25,64] — 22 in place
# Pass 4: [11,12,22,25,64] — done!

# Writing to a file ("w" = write mode — creates or overwrites)
with open("scores.txt", "w") as f:  # Opens file, auto-closes when done
    f.write("Alice,92\n")              # \n = newline character
    f.write("Bob,78\n")
    f.write("Charlie,85\n")

# Reading from a file
with open("scores.txt", "r") as f:  # "r" = read mode
    content = f.read()               # Read entire file as one string
    print(content)

# Reading line by line
with open("scores.txt", "r") as f:
    for line in f:                   # Loop through each line
        line = line.strip()          # Remove \n whitespace
        parts = line.split(",")      # Split on comma: ["Alice", "92"]
        name, score = parts[0], int(parts[1])
        print(f"{name}: {score}")

# Appending to a file (adds without deleting existing content)
with open("scores.txt", "a") as f:  # "a" = append mode
    f.write("Diana,95\n")              # Added to end of file

def check_password(password):
    """Return a strength score and feedback for a password."""
    score    = 0
    feedback = []

    # Check length
    if len(password) >= 12:
        score += 2
    elif len(password) >= 8:
        score += 1
    else:
        feedback.append("Use at least 8 characters")

    # Check for uppercase letters
    has_upper = any(c.isupper() for c in password)
    if has_upper:
        score += 1
    else:
        feedback.append("Add uppercase letters (A–Z)")

    # Check for digits
    has_digit = any(c.isdigit() for c in password)
    if has_digit:
        score += 1
    else:
        feedback.append("Add digits (0–9)")

    # Check for symbols
    symbols    = "!@#$%^&*()_-+=[]{}|;:,.<>?"
    has_symbol = any(c in symbols for c in password)
    if has_symbol:
        score += 2
    else:
        feedback.append("Add symbols (!@#$ etc)")

    # Determine strength label
    if   score >= 5: strength = "🔒 Strong"
    elif score >= 3: strength = "⚠️  Medium"
    else:             strength = "❌ Weak"

    return strength, feedback

# Main program
pwd = input("Enter a password to check: ")
strength, tips = check_password(pwd)
print(f"\nStrength: {strength}")
if tips:
    print("Suggestions:")
    for tip in tips:
        print(f"  • {tip}")

def caesar(text, shift, encode=True):
    """Encode or decode text using Caesar cipher."""
    if not encode:                    # Decoding = reverse shift
        shift = -shift
    result = ""

    for ch in text:
        if ch.isalpha():             # Only shift letters
            base = ord('A') if ch.isupper() else ord('a')
            # ord() gives ASCII number; chr() converts back to character
            # % 26 wraps around the alphabet (z → a)
            result += chr((ord(ch) - base + shift) % 26 + base)
        else:
            result += ch              # Spaces and punctuation unchanged
    return result

# Demo
msg     = "Hello World"
encoded = caesar(msg, 3)
decoded = caesar(encoded, 3, encode=False)

print(f"Original : {msg}")      # Hello World
print(f"Encrypted: {encoded}")  # Khoor Zruog
print(f"Decrypted: {decoded}")  # Hello World

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>My Page Title</title>
</head>
<body>

  <!-- ALL your visible content goes in here -->

</body>
</html>

<head>

  <!-- 1. CHARACTER ENCODING — always first inside head -->
  <meta charset="UTF-8">

  <!-- 2. VIEWPORT — makes page responsive on phones/tablets -->
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  <link rel="preconnect" href="https://fonts.googleapis.com">
  <link href="https://fonts.googleapis.com/css2?family=Inter&display=swap" rel="stylesheet">

</head>

<h1>Main Page Title — The Biggest Heading</h1>
<h2>Section Heading — Like a Chapter Title</h2>
<h3>Sub-section — Heading inside a chapter</h3>
<h4>Smaller sub-section</h4>
<h5>Rarely used — very small heading</h5>
<h6>Smallest heading level</h6>

<!-- PARAGRAPH — creates a block of text with space above and below -->
<p>This is a paragraph of text. Even if you put
   lots of spaces    or line breaks in the code,
   the browser ignores them.</p>

<!-- LINE BREAK — forces a new line within the same paragraph -->
<p>
  Line one of this paragraph.<br>
  Line two — still the same paragraph, just a new line.
</p>

<!-- HORIZONTAL RULE — a full-width dividing line -->
<hr>

<!-- TEXT FORMATTING TAGS -->
<p>
  <strong>Bold — important text</strong><br>
  <em>Italic — emphasised text</em><br>
  <u>Underlined text</u><br>
  <mark>Highlighted text — yellow background</mark><br>
  <code>print("Hello")</code> — monospace font for code
</p>

<!-- 1. EXTERNAL LINK -->
<a href="https://www.bbc.co.uk">Visit the BBC website</a>

<!-- 2. OPEN IN NEW TAB -->
<a href="https://www.google.com" target="_blank">Google (new tab)</a>

<!-- 3. ANCHOR LINK — jumps to a section on the SAME page -->
<a href="#contact-section">Jump to Contact</a>
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<h2 id="contact-section">Contact Us</h2>

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<a href="mailto:[email protected]">Email us</a>

<!-- BASIC IMAGE -->
<img src="logo.png" alt="TheShelf school logo">

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<img src="profile.jpg"
     alt="A smiling student"
     width="300"
     height="200">

<!-- CLICKABLE IMAGE — wrap <img> inside <a> -->
<a href="https://www.bbc.co.uk">
  <img src="bbc-logo.png" alt="Go to BBC">
</a>

<!-- UNORDERED LIST — bullet points -->
<ul>
  <li>Online Safety</li>
  <li>Binary Numbers</li>
  <li>Python Programming</li>
</ul>

<!-- ORDERED LIST — numbered -->
<ol>
  <li>Open your IDE</li>
  <li>Write your Python code</li>
  <li>Run and test the program</li>
</ol>

<table>
  <tr>
    <th>Name</th>
    <th>Score</th>
    <th>Grade</th>
  </tr>
  <tr>
    <td>Alice</td>
    <td>92</td>
    <td>A</td>
  </tr>
  <tr>
    <td>Bob</td>
    <td>78</td>
    <td>B</td>
  </tr>
</table>

<form action="submit.php" method="post">

  <!-- TEXT INPUT -->
  <label for="fname">First Name:</label>
  <input type="text" id="fname" name="firstname" required>

  <!-- EMAIL -->
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  <input type="email" id="email" name="email" required>

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  <label for="pwd">Password:</label>
  <input type="password" id="pwd" name="password">

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  <p>Select your year group:</p>
  <input type="radio" name="year" value="7" id="y7">
  <label for="y7">Year 7</label>
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  <!-- DROPDOWN SELECT -->
  <label for="subject">Favourite subject:</label>
  <select name="subject" id="subject">
    <option value="">-- Please choose --</option>
    <option value="computing">Computing</option>
    <option value="maths">Maths</option>
  </select>

  <!-- BUTTONS -->
  <button type="submit">Submit Form</button>

</form>

<header>
  <h1>TheShelf — Computing Resources</h1>
</header>

<nav>
  <a href="index.html">Home</a>
  <a href="year7.html">Year 7</a>
</nav>

<main>
  <section id="binary">
    <h2>Binary Numbers</h2>
    <p>Binary uses only 0s and 1s...</p>
  </section>
</main>

<footer>
  <p>&copy; 2025 TheShelf.</p>
</footer>

<!-- INLINE CSS — style directly on one tag -->
<h1 style="color: navy; text-align: center;">Blue Centred Heading</h1>

<!-- INTERNAL <style> BLOCK — inside <head> -->
<style>
  body {
    font-family: Arial, sans-serif;
    background-color: #f0f4f8;
    color: #333333;
  }
  h1 {
    color: darkblue;
    font-size: 2em;
    text-align: center;
  }
</style>

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<link rel="stylesheet" href="style.css">

<!DOCTYPE html>
<html lang="en">
<head>
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  <title>Alice Johnson — Computing Portfolio</title>
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  <header>
    <h1>Alice Johnson</h1>
    <p>Year 9 Computing Portfolio</p>
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    <a href="#about">About</a>
    <a href="#projects">Projects</a>
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    <section id="about">
      <h2>About Me</h2>
      <p>I am a Year 9 student passionate about computing.</p>
    </section>
  </main>

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    <p>&copy; 2025 Alice Johnson</p>
  </footer>

</body>
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