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6.2. else & finally statements

Apart from except, we can also use else and a finally statement with a try block. These are covered in this section.

try-except-else

An else block can be added after except block which would be executed when error does not occur.

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n1 = int(input('Enter number 1: '))
n2 = int(input('Enter number 2: '))

try:
    print(n1 / n2)
except ZeroDivisionError:
    print('number 2 cannot be zero!')
else:
    print('division successful')

Enter number 1: 8
Enter number 2: 2
4.0
division successful

Enter number 1: 8
Enter number 2: 0
number 2 cannot be zero!

This else is not executed when error is raised and except is executed.

try-except-finally

The finally block is used with try to execute the code after all the error handling is performed:

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n1 = int(input('Enter number 1: '))
n2 = int(input('Enter number 2: '))

try:
    print(n1 / n2)
except ZeroDivisionError:
    print('number 2 cannot be zero!')
finally:
    print('program ended')

Enter number 1: 8
Enter number 2: 2
4.0
program ended

Enter number 1: 8
Enter number 2: 0
number 2 cannot be zero!
program ended

The finally block is always executed at the end once all other blocks are done executing.

try-finally

try can be paired with finally without an except. In this case, the code in try block is executed and if an error occurs, finally block is executed before raising the error.

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n1 = int(input('Enter number 1: '))
n2 = int(input('Enter number 2: '))

try:
    print(n1 / n2)
finally:
    print('program ended')

Enter number 1: 8
Enter number 2: 2
4.0
program ended

Enter number 1: 8
Enter number 2: 0
number 2 cannot be zero!
program ended
Traceback (most recent call last):
  File "C:\XGuides\python\test.py", line 5, in <module>
    print(n1 / n2)
          ~~~^~~~
ZeroDivisionError: division by zero

try-except-else-finally

finally can also be applied with try-except-else.

try:
    # do something here
    ...
except Exception:
    # handle Exception here
    ...
else:
    # if no error occurs, do something here
    ...
finally:
    # regardless of error occurs or not, do this
    # at the end
    ...

Order of blocks

Following rules should must be followed for order of try, except, else and finally blocks:

  • The first block is always try.
  • else can only be added when except is used.
  • else is always put after all the except blocks.
  • finally is always the last block.

In short, the only valid blocks order are:

  • try-except
  • try-except-else
  • try-except-else-finally
  • try-except-finally
  • try-finally