Python Programming! Error Handling | Lectures 13

Let’s Start Python Programming for Beginners to Advanced. Error Handling, Lectures 13

Table of Contents

🐍 Lecture 13: Error Handling

🎯 Goal

By the end of this lecture, you will:

Understand what errors are and why they happen.
Be able to use try and except to catch and handle errors.
Know how to write programs that don’t crash when something goes wrong.
Build a simple program that handles user input safely.

🧠 What Are Errors?

Sometimes, your code might run into a problem, like trying to divide by zero or asking for a number but getting a word instead.

These problems are called errors, and Python usually stops running your program when it finds one.

But with error handling, we can prepare for these mistakes and tell Python what to do if they happen.

🧠 Think of error handling like training wheels on a bike — it helps your program stay upright even when something goes wrong!

🔁 Using `try` and `except`

We use the try and except blocks to catch errors and respond to them gracefully.

Syntax:

try:
    # Try to do something
except:
    # If there's an error, do this instead

Example:

try:
    x = int(input("Enter a number: "))
    print(10 / x)
except:
    print("Something went wrong!")

👉 This will handle any error, like if the user types a word instead of a number or tries to divide by zero.

❗ Specific vs General Error Handling

You can also handle specific errors:

Example: Handle Division by Zero

try:
    x = int(input("Enter a number: "))
    print(10 / x)
except ZeroDivisionError:
    print("You can't divide by zero!")

Example: Handle Invalid Input

try:
    x = int(input("Enter a number: "))
    print(10 / x)
except ValueError:
    print("That's not a valid number!")

You can even combine multiple exceptions:

try:
    x = int(input("Enter a number: "))
    print(10 / x)
except ValueError:
    print("Please enter a valid number.")
except ZeroDivisionError:
    print("You can't divide by zero.")

✅ The `else` and `finally` Clauses

You can also use else and finally with try-except.

else Runs only if no errors occurred.
finally Always runs at the end, whether there was an error or not.

try:
    num = int(input("Enter a number: "))
    result = 100 / num
except ValueError:
    print("That's not a number!")
except ZeroDivisionError:
    print("Can't divide by zero!")
else:
    print("Result:", result)
finally:
    print("Thank you for using the calculator!")

🧪 Try It Yourself!

Write a program that:

Asks the user to enter their age.
Converts it to an integer.
Prints a message like "You are X years old."
Handles invalid input gracefully.

💡 Sample Code:

try:
    age = int(input("Enter your age: "))
    print(f"You are {age} years old.")
except ValueError:
    print("That's not a valid age. Please try again.")

🚀 Challenge (Optional)

Make a safe calculator that keeps asking for numbers until valid input is given.

Example:

while True:
    try:
        num = int(input("Enter a number: "))
        print("Your number squared is:", num ** 2)
        break
    except ValueError:
        print("Invalid input! Please enter a number.")

This loop keeps running until the user enters a valid number.