Python Error Handling Explained | Try, Except, Else & Finally

• What is Error Handling?

  • Error Handling is the process of handling runtime errors without stopping the program.
  • Instead of crashing, the program can display a meaningful message or perform another action.

Example Without Error Handling

num = int(input("Enter a number: ")) 
result = 10 / num 
print(result)

Output:

ZeroDivisionError: division by zero

• Why Use Error Handling?

  • Error handling helps you:

1. Prevent program crashes

2. Improve user experience

          3. Display meaningful error messages

4. Handle unexpected situations

5. Write professional applications

• The try Block

  • The code that may cause an error is placed inside the try block.

    try: number = int(input("Enter a number: ")) print(number)

If an exception occurs, Python immediately looks for an except block.

• The except Block

  • The except block handles the exception.

try:
 	number = int(input("Enter a number: "))
  	print(10 / number) 
except ZeroDivisionError: 
 	 print("Cannot divide by zero.")

• Handling Multiple Exceptions

  • A program can raise different types of exceptions.

try:
 	number = int(input("Enter a number: "))
  	print(10 / number) 

except ValueError: 
	print("Please enter a valid number.") 

except ZeroDivisionError: 
	print("Zero is not allowed.")

• Catching Multiple Exceptions Together

try: 
	number = int(input("Enter a number: "))
	print(10 / number) 
	
except (ValueError, ZeroDivisionError): 
	print("Invalid input.")

• Generic Exception

  • If you don't know which exception may occur

try: 
	number = int(input()) 
	print(10 / number) 
	
except Exception as error: 
	print(error)

Example Output:

division by zero

or

invalid literal for int()

• The else Block

  • The else block executes only if no exception occurs.

try: 
	number = int(input("Enter a number: "))
	print(10 / number) 

except ZeroDivisionError: 
	print("Cannot divide by zero.")

else: 
	print("Program executed successfully.")

Output:

Enter a number: 2

5.0
Program executed successfully.

• The finally Block

  • The finally block always executes, whether an exception occurs or not.

try:
    file = open("sample.txt")

except FileNotFoundError:
    print("File not found.")

finally:
    print("Program finished.")

Output:

File not found.
Program finished.

• Using raise

  • The raise keyword lets you create your own exceptions.

age = -5

if age < 0:
    raise ValueError("Age cannot be negative.")

Output:

ValueError: Age cannot be negative.