Python Exception Handling: Try‑Except, Else, Finally, and Raising Exceptions

Python provides a structured way to handle runtime errors using the try , except , else , and finally statements. The simplest form catches any exception:

try:
    # code that may raise an exception
except:
    # handle the error

Specific exception types can be targeted to provide tailored responses:

try:
    num = int(input("Enter an integer: "))
except ValueError:
    print("Please enter a valid number!")
except ZeroDivisionError:
    print("Math error")

A more comprehensive example asks the user for an integer, divides 8 by that number, and handles both ZeroDivisionError and ValueError :

while True:
    try:
        # Prompt user for an integer
        num = int(input("Enter an integer: "))
        result = 8 / num
        print(result)
    except ZeroDivisionError:
        print("Math error")
    except ValueError:
        print("Please enter a number")

Exceptions propagate up the call stack. If a function raises an error and it is not caught locally, the caller can handle it:

def demo1():
    return int(input("Enter integer: "))

def demo2():
    return demo1()

try:
    print(demo2())
except Exception as e:
    print(f"Program encountered an error: {e}")

Custom exceptions can be raised deliberately using the raise statement. The following function validates a password length and raises an exception if it is too short:

def input_password():
    pwd = input("Enter password: ")
    if len(pwd) >= 8:
        return pwd
    else:
        print("Raising exception!")
        ex = Exception("Password length insufficient!")
        raise ex

try:
    print(input_password())
except Exception as e:
    print(e)

The complete syntax for exception handling combines all parts:

try:
    # code that may raise an exception
except SpecificError1:
    # handle error type 1
except (SpecificError2, SpecificError3):
    # handle error types 2 and 3
except Exception as e:
    # handle any other exception
    print(e)
else:
    # executed if no exception occurs
    pass
finally:
    # always executed
    print("This runs regardless of exceptions")

These examples illustrate the fundamental techniques for managing errors in Python programs.