Programming with Python – Complete Study Guide 2026 Latest Updated for beginners

UNIT 9 – PYTHON PROGRAMMING (A/L ICT Sri Lanka)
Complete guide covering Introduction to Programming, Algorithms, Flowcharts, Python Fundamentals, Control Structures, Data Structures, Functions, File Handling, and Error Handling. This covers the core theory expected for Unit 9 and aligns perfectly with the Sri Lankan A/L ICT syllabus.

9.1 Introduction to Programming

Basic Definitions

• Program: A set of instructions given to a computer to perform a task.
• Programming: The process of writing, testing, debugging, and maintaining computer programs.

Why Programming? Automates tasks, solves problems efficiently, reduces human errors, and saves time.

Programming Languages

• 1GL (Machine Language): Binary code (e.g., 10110011). Fast execution but difficult to understand and error-prone.
• 2GL (Assembly Language): Uses mnemonics (e.g., MOV A,10). Requires an Assembler.
• 3GL (High-Level Languages): Python, Java, C++, Pascal. Easy to read, easy debugging, and portable. (Python belongs to this category).

Language Translators

Feature	Compiler (C, C++)	Interpreter (Python)
Translation	Whole program at once	Line by line
Execution Speed	Faster	Slower
Object Code	Generates object code	No object code
Debugging	Harder	Easier

A/L Exam Question: Python uses which translator?
Answer: Interpreter.

9.2 Algorithms

Definition & Characteristics

An algorithm is a finite sequence of instructions for solving a problem.

• Input: Accepts data (e.g., INPUT A).
• Output: Produces result (e.g., PRINT SUM).
• Definiteness: Every step must be clear.
• Finiteness: Must end after finite steps.
• Effectiveness: Each step must be practical.

Example: Add Two Numbers

START
INPUT A
INPUT B
SUM ← A + B
PRINT SUM
STOP

Control Structures

1. Sequence: Instructions executed one after another.

INPUT A, B
SUM = A + B
PRINT SUM

2. Selection: Decision making.

IF MARK >= 50 THEN
   PRINT PASS
ELSE
   PRINT FAIL
ENDIF

3. Iteration: Repeating instructions.

FOR I = 1 TO 5
   PRINT I
NEXT I

9.3 Flowcharts

Definition

A graphical representation of an algorithm using standard symbols.

Standard Symbols

Symbol Shape	Purpose
Oval	Start / Stop
Rectangle	Process (Calculations)
Parallelogram	Input / Output
Diamond	Decision (Yes/No)
Arrow	Flow Direction

Example: Find Area of Rectangle

START
  ↓
INPUT L, W
  ↓
AREA = L × W
  ↓
PRINT AREA
  ↓
STOP

9.4 Python Fundamentals

Features & First Program

Features: Simple syntax, Interpreted language, Open source, Cross-platform.

# First Python Program
print("Hello World")

Comments

# Single line comment

"""
Multi-line 
comment
"""

Variables & Naming Rules

Variables store data. Valid: student, student_name, age1. Invalid: 1age, student-name, class.

name = "Amal"
age = 18

Data Types

• Integer: x = 10
• Float: x = 10.5
• String: name = "Kamal"
• Boolean: status = True

Input and Output

# Input
name = input("Enter name:")
age = int(input())      # Integer input
salary = float(input()) # Float input

# Output
print(name)

Operators in Python

Arithmetic Operators

Operator	Meaning
+	Add
-	Subtract
*	Multiply
/	Divide
//	Integer Division
%	Modulus (Remainder)
**	Power

Example: print(10 % 3) outputs 1.

Relational Operators

Operators: ==, !=, >, <, >=, <=

Example: 10 > 5 outputs True.

Logical Operators

Operators: and, or, not

Example: 5 > 2 and 4 < 8 outputs True.

Selection Statements & Loops

Selection (IF Statements)

# Simple IF
mark = 70
if mark >= 50:
    print("Pass")

# IF ELSE
mark = 45
if mark >= 50:
    print("Pass")
else:
    print("Fail")

# IF ELIF ELSE
mark = 80
if mark >= 75:
    print("A")
elif mark >= 65:
    print("B")
else:
    print("C")

Loops (Iteration)

# For Loop
for i in range(5):
    print(i) 
# Output: 0, 1, 2, 3, 4

# While Loop
i = 1
while i <= 5:
    print(i)
    i = i + 1

Data Structures: Strings & Lists

Strings

name = "Python"

# Indexing (Starts at 0)
print(name[0])  # Output: P

# Length
print(len(name)) # Output: 6

Lists

# Creating & Accessing
marks = [45, 67, 89]
print(marks[0])  # Output: 45

# Updating
marks[1] = 90

List Methods

• marks.append(100) - Adds to the end
• marks.insert(1, 50) - Inserts at index 1
• marks.remove(67) - Removes value 67
• marks.sort() - Sorts ascending
• marks.reverse() - Reverses the list

Functions

Function Types

# 1. Without Parameters
def display():
    print("ICT")
display() # Calling the function

# 2. With Parameters
def add(a, b):
    print(a + b)

# 3. With Return Value
def add(a, b):
    return a + b
result = add(5, 10)

File Handling

Opening Files

f = open("data.txt", "r")  # Read Mode
f = open("data.txt", "w")  # Write Mode
f = open("data.txt", "a")  # Append Mode

Reading, Writing & Closing

# Write to file
f.write("Hello")

# Read from file
data = f.read()

# Always close the file
f.close()

Errors in Python

• Syntax Error: Violates grammar rules.
  Example: if x > 5 (Missing colon at the end).
• Runtime Error: Occurs during execution.
  Example: 10 / 0 (Division by zero).
• Logical Error: Program runs but produces incorrect output.
  Example: Using area = length + width instead of area = length * width.

🌟 Frequently Asked A/L Questions

Q1: What are the three control structures?
Answer: 1. Sequence, 2. Selection, 3. Iteration.

Q2: Differentiate Compiler and Interpreter.

Compiler	Interpreter
Whole program translated	Line by line
Faster execution	Slower execution
Generates object code	No object code

Q3: Write a Python program to find the largest of two numbers.

a = int(input())
b = int(input())

if a > b:
    print(a)
else:
    print(b)

Q4: Write a program to print numbers from 1 to 10.

for i in range(1, 11):
    print(i)

Q5: Create a list and print all values.

num = [10, 20, 30, 40]

for x in num:
    print(x)

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