Basic Exception Handling: try-except¶

Exception handling allows your program to handle errors gracefully instead of crashing.

The try-except Block¶

try:
    # Code that might raise an exception
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")

Catching Multiple Exceptions¶

try:
    num = int(input("Enter a number: "))
    result = 10 / num
    print(f"Result: {result}")
except ValueError:
    print("Please enter a valid number")
except ZeroDivisionError:
    print("Cannot divide by zero")

The else Clause¶

The else block executes if no exception occurs.

try:
    num = int(input("Enter a number: "))
    result = 10 / num
except ValueError:
    print("Invalid input")
except ZeroDivisionError:
    print("Cannot divide by zero")
else:
    print(f"Result: {result}")

The finally Clause¶

The finally block always executes, regardless of whether an exception occurred.

try:
    file = open("example.txt", "r")
    content = file.read()
    print(content)
except FileNotFoundError:
    print("File not found")
finally:
    file.close()  # This always runs

Common Exceptions¶

ValueError : Invalid value for a data type
TypeError : Operation on incompatible types
IndexError : Accessing invalid index
KeyError : Accessing non-existent dictionary key
FileNotFoundError : File not found
ZeroDivisionError : Division by zero

Raising Exceptions¶

You can raise exceptions manually.

def check_age(age):
    if age < 0:
        raise ValueError("Age cannot be negative")
    return age

try:
    check_age(-5)
except ValueError as e:
    print(e)

Best Practices¶

Catch specific exceptions rather than using bare except
Use finally for cleanup operations
Don’t overuse exception handling for normal flow control
Provide meaningful error messages