chapter-10.2-exception-handling.md

Exception Handling in python

Exceptions are generally not handled by default and needs handling by writing the code within try ... except blocks.

Steps of handling the exception

1. First, try executing the statement(s) inside the try block.
2. If the error exists write the program to handle exception in the except block.
3. Optionally, we can do certain tasks even if error does not occur.

We can use try, except, finally and else statements for handling different kinds of exceptions.

• try block is used to try executing our statements
• except block handles error during execution. We can have multiple except blocks for a try statement.
• else block executes whenever error does not occur
• finally block executes under all circumstances. This block is also known as clean-up block.

The following example shows how to handle the ZeroDivisionError using try ... except blocks:

a = 10
b = 0
try:
    print(a/b)
except:
    print("Hey!! Here comes an error")

Handling multiple exceptions

We can use multiple except blocks by specifying different exceptions.

The following function shows how to handle multiple exceptions:

def divide(a, b):
    try:
        print(f"I'm trying to solve the problem: {a} / {b}")
        x = a / b
        print("Hey I solved it")
        return x

    except ZeroDivisionError:
        print("Hey Here comes an error : Zero Division Error")

    except TypeError as e:
        print(f"Error Spotted..{e}")

    except Exception as e:
        print(f"An Unknown Error occured. The error is: {e}")

divide('abc', 'x')    # TypeError is handled
divide(1, 0)        # ZeroDivisionError is handled

Handling errors with try, except, else, and finally blocks

list1 = [6, 8, 9, 'John', 'Doe']

def print_index(index: int):
    value = None
    try:
        value = list1[index]
    except IndexError:
        print('There is an error, the index is out of range, the last value would be printed')
        value = list1[-1]
    else:   # this executes only when no error occurs
        print("I did not find any error")

    finally:        # This always execute at the end
        print(f"I Handled the exception when occured. The value is: {value}")


print_index(3)  # runs the `try` block then `else` block and then `finally` block at the end.
print_index(8)  # runs the `try` block, then `IndexError` block and then `finally` block at the end.

Catching Multiple exceptions in the single except block

We can catch multiple exceptions by calling them as the tuple of exceptions.

try:
    x = a / b
except (TypeError, ZeroDivisionError) as e:
    print(f"Error Spotted..{e}")

The above except code block catches both TypeError and ZeroDivisionError without needing to create different catch blocks.