Exception Handling in Python – Managing Errors Gracefully

Introduction

Errors are part of programming — no matter how perfect your code seems.
In Python, when an error occurs during execution, the program stops and shows an error message.
But with exception handling, you can catch and manage these errors smoothly.

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1. What Is an Exception?

An exception is an error that occurs during program execution, disrupting the normal flow.

Examples include:

• ZeroDivisionError – dividing by zero

• ValueError – invalid input

• FileNotFoundError – missing file

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2. Basic try–except Block

Example:

try:
    a = int(input("Enter a number: "))
    b = int(input("Enter another number: "))
    print("Result =", a / b)
except ZeroDivisionError:
    print("You can’t divide by zero!")

Output:

Enter a number: 10
Enter another number: 0
You can’t divide by zero!

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3. Handling Multiple Exceptions

try:
    num = int(input("Enter a number: "))
    print(10 / num)
except ZeroDivisionError:
    print("Cannot divide by zero!")
except ValueError:
    print("Invalid input. Please enter a number.")

Output:

Invalid input. Please enter a number.

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4. Using else Block

The else block runs only if no error occurs.

try:
    num = int(input("Enter a number: "))
    print("Square =", num * num)
except ValueError:
    print("Please enter a valid number.")
else:
    print("Execution successful!")

Output:

Enter a number: 5
Square = 25
Execution successful!

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5. Using finally Block

The finally block always executes — useful for closing files or releasing resources.

try:
    f = open("demo.txt", "w")
    f.write("Learning Python Exception Handling")
finally:
    f.close()
    print("File closed successfully.")

Output:

File closed successfully.

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6. Raising Exceptions Manually

You can raise an exception intentionally using the raise keyword.

x = -1
if x < 0:
    raise ValueError("Negative numbers not allowed!")

Output:

ValueError: Negative numbers not allowed!

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7. Common Built-in Exceptions

Exception	Description
ZeroDivisionError	Divide by zero
ValueError	Wrong type of value
FileNotFoundError	File doesn’t exist
TypeError	Wrong data type
IndexError	Invalid index
KeyError	Missing key in dictionary

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8. Nested try–except Example

try:
    a = int(input("Enter first number: "))
    b = int(input("Enter second number: "))
    try:
        result = a / b
        print("Result:", result)
    except ZeroDivisionError:
        print("Division by zero error!")
except ValueError:
    print("Invalid input!")

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Challenge for You

Write a program that:

• Takes two numbers as input

• Prints their division result

• Handles both ValueError and ZeroDivisionError gracefully

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Final Thoughts

• Exceptions make your program robust
• Use try–except to prevent crashes
• finally helps you clean up resources
• Use raise to customize error messages

In the next lesson, we’ll cover Object-Oriented Programming (OOP) in Python, one of the most powerful concepts in modern coding.