Exception Handling¶

Exceptions are errors that occur during program execution.

Python provides try, except, else, and finally to handle errors gracefully.

Basic try-except¶

try:
    result = 10 / 0
except:
    print("An error occurred")

Catch Specific Exceptions¶

It is better to catch specific errors.

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

Multiple Exceptions¶

try:
    value = int("abc")
except ZeroDivisionError:
    print("Division error")
except ValueError:
    print("Invalid value")

else Block¶

Runs only if no exception occurs.

try:
    result = 10 / 2
except ZeroDivisionError:
    print("Error")
else:
    print("Success:", result)

Output¶

Success: 5.0

finally Block¶

Always runs, whether there is an error or not.

try:
    file = open("test.txt", "r")
    content = file.read()
except FileNotFoundError:
    print("File not found")
finally:
    print("Execution finished")

Raising Exceptions¶

You can manually raise errors using raise.

age = -1

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

Custom Exception Handling Pattern¶

def divide(a, b):
    if b == 0:
        raise ValueError("b cannot be zero")
    return a / b

try:
    print(divide(10, 0))
except ValueError as e:
    print("Error:", e)

Common Built-in Exceptions¶

Exception	Description
ValueError	Invalid value
TypeError	Wrong type
ZeroDivisionError	Division by zero
FileNotFoundError	Missing file
IndexError	Invalid list index

Summary¶

Use try to wrap risky code
Use except to handle errors
Use else for success flow
Use finally for cleanup
Use raise to trigger exceptions manually

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