intermediate

Try-Except Error Handling

Handle errors gracefully with Python exception handling.

Errors happen in every program. Maybe a file does not exist, a user enters invalid input, or a network request fails. Exception handling with try-except lets your program respond to errors gracefully instead of crashing. This is a critical skill for building robust, production-ready applications.

📚 Concepts & Theory

Basic Try-Except

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")

Catching Multiple Exceptions

try:
    value = int(input("Enter a number: "))
    result = 10 / value
except ValueError:
    print("That is not a valid number")
except ZeroDivisionError:
    print("Cannot divide by zero")

The else Clause

Runs if no exception occurred:

try:
    number = int("42")
except ValueError:
    print("Invalid number")
else:
    print(f"Success! Got {number}")

The finally Clause

Always runs, even if an exception occurred:

try:
    file = open("data.txt")
    data = file.read()
except FileNotFoundError:
    print("File not found")
finally:
    file.close()  # Always close the file

Catching Any Exception

try:
    risky_operation()
except Exception as e:
    print(f"Error: {e}")

🎯 Your Challenge

Write code that tries to convert the string "hello" to an integer using int(). Catch the ValueError and set a variable `result` to 0 if the conversion fails. If it succeeds, set `result` to the converted value.

📝 Starter Code

Python

# Try to convert "hello" to integer
text = "hello"

try:
    result = 
except ValueError:
    result =

Put the risky operation inside try
ValueError is raised for invalid conversions
The except block only runs if an error occurs
Set your fallback value in the except block

Solution

Python

text = "hello"

try:
    result = int(text)
except ValueError:
    result = 0

Explanation

We try to convert "hello" to an integer with int(text). Since "hello" is not a valid number, Python raises a ValueError. The except block catches this error and sets result to 0 as a fallback.

⚠️ Common Mistakes to Avoid

Catching too broad exceptions (bare except)
Not handling specific exception types
Putting too much code in the try block
Forgetting that except runs only if an exception occurs

❓ Frequently Asked Questions

Generally no. Catch specific exceptions you expect. Catching everything can hide bugs and make debugging harder.

except runs only when an exception occurs. finally always runs, whether there was an exception or not.