LESSON 4: Getting started with PYTHON

Python is known for its clean and simple syntax. That means fewer symbols and punctuation marks compared to many other programming languages like Java or C++.

1. Comments

Comments are completely ignored by the interpreter. They are meant for fellow programmers. In Python, there are two types of comments:

• Single-line comment - use #

• Multi-line comment - use either ''' or """

Python Code

#My first Python code

print("Hello, World!")

"""

This is a comment

written in

more than just one line

"""

✅ Try It:

Open Google Colab, create a new notebook, and run the examples above in new code cells.

2. Indentation

Indentation refers to the spaces at the beginning of line of code (use space bar or tab). Python uses indentation to indicate a block of code.

Python Code

if 5 > 3:

 print("Five is greater than three")

if 5 > 3:

 print("Five is greater than three")

 if 10 > 3:

   if 15 > 3:

     print("All numbers are greater than 3")

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Run the examples above in new code cells.

3. Lines

Backslash can be used to place long statements on multiple lines. Semicolon can be used to put multiple short statements on the same line.

Python Code

#This is a long statement broken into two lines by using a backslash

result = 1 + 2 + 3 + 4 + \

5 + 6 + 7 + 8 + 9

print(result)

#These are two short statements placed on the same line using a semicolon

name = "Aminah"; age = 30; print(name, age)

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Run the examples above in new code cells.

4. Semicolons

Statements end at the end of the line. No semicolons used in the codes to indicate the end of the line. 

Python Code

#No semicolon at the end of line

print("Hello")

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A variable is like a container that holds a value. Python has no command for declaring a variable.

1. Must start with a letter or underscore (_)

2. Cannot start with a number

3. Use lowercase letters and underscores (e.g., total_score)

4. Cannot use reserved Python keywords like if, print, True

Python Code

x = 3 

y = "Hello"

print(x)

print(y)

#Good variable names 

student_name = "Aida"

age = 15

#Bad variable names

2name = "Ali"        # ❌ Invalid: starts with a number

class = "English"    # ❌ Invalid: 'class' is a keyword

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Assigning a value to a variable is done using the assignment operator (=).

Assignments can be done on more than one variable "simultaneously" on the same line or assign the same value to multiple variable.

Python Code

#assign values to multiple variable

x, y, z = 5,10,15

print(x)

print(y)

print(z) 

#assign the same value to multiple variable

a = b = c = 3

d = 6

print(a)

print(b)

print(c)

print(d) 

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Arithmetic operations can be performed and directly assign the result to a variable. These operations are commonly used when you want to store or update values during a program's execution.

Python Code

# Addition (+)

x = 5

y = 10

print(x + y)

a = 3 + 6

print(a)

# Subtraction (-)

b = 5 - 2

print(b)

# Multiplication (*)

c = 2 * 4

print(c)

# Division (/)

d = 15 / 3

print(d)

# Modulus (%)

e = 7 % 3

print(e)

# Floor Division (//)

g = 7 // 3

print(g)

# Exponent (**)

f = 2 ** 4

print(f)

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Run the examples above in new code cells.

Python automatically detects the type of value you assign to a variable.

1. Numbers 

Python supports integers (whole number), floats (decimal number), and complex numbers.

Python Code

x = 5       # int

y = 3.14    # float

z = 1 + 2j  # complex

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2. String

Strings are sequences of characters. String variables can be declared either using single ' or double " quotes.

Python Code

name = "Alice"

print(name)

mystring1 = 'Hello world!'

mystring2 = "Hello world!"

print(mystring1)

print(mystring2)

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3. Boolean

A Boolean data type in Python has only two possible values:  True or False

These are often used in conditional statements, comparisons, and logic operations.

Python Code

x = True

y = False

print(y)      # Output: False

is_sunny = True

is_raining = False

print(is_sunny)      # Output: True

# +++ Python automatically returns a Boolean when you perform a comparison +++

# Equal (==)

result1 = 5 == 5

print(result1)

# Not Equal (!=)

result2 = 5 != 5

print(result2)

# Greater Than (>)

result3 = 5 > 3

print(result3)

# Less Than (<)

result4 = 5 < 3

print(result4)

# Greater Than or Equal To (>=)

result5 = 5 >= 3

print(result5)

# Less Than or Equal To (<=)

result6 = 5 <= 3

print(result6)

# +++ some functions return Boolean values +++

name = "Ali"

print(name.isalpha())   # True - only letters

number = "1234"

print(number.isdigit()) # True - only digits

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Function type() to get the data type of a variable.

Python Code

x = 3

y = 3.0

z = "Hello"

print(type(x))

print(type(y))

print(type(z))

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If you want to specify the data type of a variable, this can be done with casting. Casting means using constructor functions to change the data type of a variable.

Python Code

x = int(3.7)     # Float to int

print(x)         # Output: 3

y = int("10")    # String to int

print(y)         # Output: 10

# If the string cannot be converted to an integer (e.g., "ten"), it will raise an error

# int("ten")  # ❌ This will cause an error

a = float(5)      # Integer to float

print(a)          # Output: 5.0

b = float("12.34") # String to float

print(b)          # Output: 12.34

name = str(100)

print(name)        # Output: "100"

print(type(name))  # Output: <class 'str'>

greeting = "Hello " + str(2025)

print(greeting)  # Output: Hello 2025

print(bool(1))      # True

print(bool(0))      # False

print(bool(""))     # False (empty string)

print(bool("Hi"))   # True (non-empty string)

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Why use Casting?

1. To prepare input from users

Python Code

age = int(input("Enter your age: "))  # Convert user input to int

2. To fix data format from APIs or files

Python Code

temperature = float("25.5")  # Convert string from file to float

3. To force a specific format in calculations

Python Code

total = float(3) + 2.5

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Python Collection Data Types are used to group multiple items into a single variable. Each collection type has its own structure, behavior, and purpose.

Lists, tuples, sets, and dictionaries are built-in data types in Python. They are all collection data types that is used to store multiple values in a single variable.

1. List

A list is a mutable, ordered collection of items.

🔹 List Characteristics:

• Defined using square brackets [ ]

• Items are indexed starting at 0

• Items have a fixed order

• Items can be added, changed, or removed

• Can store different data types together

• Allows duplicates

Python Code

fruits = ["apple", "banana", "cherry"]

print(fruits[1])  # Output: banana

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Insert Item(s) into a List

🔹 .appent() - adds an item to the end of list

Python Code

fruits = ["apple", "banana", "cherry"]

fruits.append("orange")  # Add item

print(fruits)            # Output: ['apple', 'banana', 'cherry', 'orange']

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🔹 .insert(index,item) - inserts an item at a specific index

Python Code

fruits = ["apple", "banana", "cherry", "orange"]

fruits.insert(1,"grapes")  # Insert item into index 1

print(fruits)              # Output: ['apple', 'grapes', 'banana', 'cherry', 'orange']

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🔹 .extend(iterable) - adds multiple items from another interable (eg:list, tuple) to the end of the list

Python Code

fruits = ["apple", "banana", "cherry", "orange"]

fruits.insert(1,"grapes")  # Insert item into index 1

print(fruits)              # Output: ['apple', 'grapes', 'banana', 'cherry', 'orange']

fruits.extend(["papaya","watermelon"])  # Insert items at the end

print(fruits)          # Output: ['apple', 'grapes', 'banana', 'cherry', 'orange', 'papaya', 'watermelon']

✅ Try It:

Run the examples above in new code cells.

Removing Items from a List

🔹 .remove() - removes the first occurrence of the list

Python Code

fruits = ["apple", "banana", "cherry", "orange", "banana", "papaya", "watermelon"]

fruits.remove("banana")  # removes first occurrence of item banana

print(fruits)         

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🔹 .pop(index) - removes item at given index (default:last), returns the removed item, useful if want to use removed value

Python Code

fruits = ["apple", "banana", "cherry", "orange", "banana", "papaya", "watermelon"]

remove_item = fruit.pop(1)

print(remove_item)  

print(fruits)         

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🔹 del - deletes an item by index or a slice of items, does not return the value, can also delete entire lists or variables. 

Python Code

fruits = ["apple", "banana", "cherry", "orange", "banana", "papaya", "watermelon"]

del fruits[0] 

print(fruits)    

del fruits[:]     # deletes all item. Output: [] 

print(fruits) 

del fruits        # deletes the variable. 

# Trying to print(fruits) after del fruits. Will raise an error because the variable is gone. 

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🔹 .clear() - removes all items from the list or other collection (like set and dictionary) 

Python Code

fruits = ["apple", "banana", "orange"]

fruits.clear()

print(fruits)  # Output: [] 

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2. Tuple

A tuple is like a list, but immutable (cannot be changed after creation).

🔹 Tuple Characteristics:

• Defined using parentheses ()

• Item have a fixed order

• Cannot be modified after creation 

• Faster than lists

• Allows duplicates

Python Code

dimensions = (10, 20)

print(dimensions[0])  # Output: 10

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In Python, cannot add or delete individual items from a tuple because tuples are immutable. You can only (1) reassign the whole tuple or (2) delete the entire tuple variable.

🔹 Reassign the whole tuple

Python Code

my_tuple = ("apple", "banana", "cherry")

new_tuple = my_tuple + ("orange",)  # Adding item

print(new_tuple)  # Output: ('apple', 'banana', 'cherry', 'orange')        

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🔹 Delete the entire tuple variable

Python Code

my_tuple = (1, 2, 3)

del my_tuple

# print(my_tuple)  # ❌ NameError: name 'my_tuple' is not defined       

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3. Set

A set is an unordered collection of unique items.

🔹 Set Characteristics:

• Defined using curly braces {}

• Items are unordered - no indexing 

• Can add / remove items

• No duplicates (Useful for removing duplicates or checking membership)

Python Code

numbers = {1, 2, 3, 3, 4}

print(numbers)  # Output: {1, 2, 3, 4} — duplicates removed

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Insert Item(s) into a Set

🔹 .add(item) – Adds a single item to the set.

If the item already exists, it does nothing because sets do not allow duplicates.

Python Code

fruits = {"apple", "banana"}

fruits.add("orange")

print(fruits)  # Output: {'apple', 'banana', 'orange'}

fruits.add("apple")  # Won't add 'apple' again

print(fruits)  # Output: {'apple', 'banana', 'orange'}

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🔹 .update(iterable) – Adds multiple items from an iterable (list, tuple, or another set).

New elements are added one by one, and duplicates are ignored.

Python Code

fruits = {"apple", "banana"}

fruits.update(["orange", "grape"])

print(fruits)  # Output: {'apple', 'banana', 'orange', 'grape'}

fruits.update({"melon", "apple"})

print(fruits)  # Output: {'apple', 'banana', 'orange', 'grape', 'melon'}

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Remove Item(s) into a Set

🔹 .remove(item) – Removes an item from the set.

If the item is not found, it raises a KeyError.

Python Code

fruits = {"apple", "banana", "orange"}

fruits.remove("banana")

print(fruits)  # {'apple', 'orange'}

# fruits.remove("grape")  # KeyError: 'grape'

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🔹 .discard(item) – Removes an item, but does not raise an error if the item is not found.

Python Code

fruits = {"apple", "banana", "orange"}

fruits.discard("banana")

print(fruits)  # Output: {'apple', 'orange'}

fruits.discard("grape")  # No error even though 'grape' is not in the set

print(fruits)  # Output: {'apple', 'orange'}

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🔹 .pop() – Removes and returns an arbitrary item from the set.

Since sets are unordered, there is no guarantee of which item will be removed.

Python Code

fruits = {"apple", "banana", "orange"}

removed_item = fruits.pop()

print(removed_item)  # Random item, e.g., 'apple'

print(fruits)        # Output: Remaining items

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🔹 clear() – Removes all items from the set.

Python Code

fruits = {"apple", "banana", "orange"}

fruits.clear()

print(fruits)  # Output: set()

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🔹 del – Deletes the entire set.

Python Code

fruits = {"apple", "banana", "orange"}

del fruits

# print(fruits)  # NameError: name 'fruits' is not defined

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4. Dictionary

A dictionary stores data in key-value pairs.

🔹 Dictionary Characteristics:

• Defined using curly braces {} with key : value format

• Keys must be unique

• Ordered (as of Python 3.7+)

• Can change or update values

• Values can be of any data type

• Useful for structured data (like JSON)

Python Code

# Example dictionary

student = {

   "name": "Ali",

   "age": 12,

   "class": "6A"

}

print(student["name"]) # Output: Ali

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Insert Item(s) into a Dictionary

🔹 Using bracket notation (most common)

Python Code

student["school"] = "SK Kajang"

print(student) # Output: {'name': 'Ali', 'age': 12, 'class': '6A', 'school': 'SK Kajang'}

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🔹 .update() – Can add one or more items at once.

Python Code

student.update({"grade": "A"})

student.update({"hobby": "badminton", "height": 140})

print(student)

# Output: {'name': 'Ali', 'age': 12, 'class': '6A', 'school': 'SK Kajang', 'grade': 'A', 'hobby': 'badminton', 'height': 140}

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Remove Item(s) into a Dictionary

🔹 del keyword - Removes item by key.

Python Code

del student["class"]

print(student)

# Output: {'name': 'Ali', 'age': 12, 'school': 'SK Kajang', 'grade': 'A', 'hobby': 'badminton', 'height': 140}

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🔹 .pop(key) – Removes and returns the value.

Python Code

age = student.pop("age")

print(age) # 12

print(student) 

# Output: {'name': 'Ali', 'school': 'SK Kajang', 'grade': 'A', 'hobby': 'badminton', 'height': 140}

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🔹 .popitem() – Removes and returns the last inserted item (Python 3.7+).

Python Code

last = student.popitem()

print(last)    # Output: ('height', 140)

print(student) # Output: {'name': 'Ali', 'school': 'SK Kajang', 'grade': 'A', 'hobby': 'badminton'}

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🔹 .popitem() – Removes and returns the last inserted item (Python 3.7+).

Python Code

last = student.popitem()

print(last)    # Output: ('height', 140)

print(student) # Output: {'name': 'Ali', 'school': 'SK Kajang', 'grade': 'A', 'hobby': 'badminton'}

✅ Try It:

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🔹 .clear() – Removes all items.

Python Code

student.clear()

print(student)  # Output: {}

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🔹 del - Delete the whole dictionary.

Python Code

del student

# print(student)  # ❌ NameError: name 'student' is not defined

✅ Try It:

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🧠 Answer these to test your understanding.

1. Which of the following is a valid variable name?

A) 3total

B) userName

C) def

D) print

2. What is the type of the following value: 42.0?

A) int

B) str

C) float

D) bool

3. What will this code output?

x = True

print(type(x))

A) <class 'bool'>

B) <class 'str'>

C) <class 'int'>

D) <class 'float'>

🔧 Instructions:

1. Open Google Colab.  

2. Create a new notebook.

3. Practice the example codes in sections (1) Python Syntax, (2) Variables, (3) Data Types

4. Write a small program that:

• Stores your name, age, and student status in variables

• Prints all the values with a label

• Displays the data type of each variable