try … finally

• The try statement has optional finally clause that must be executed under all circumstances. For example:

  >>> try:
  ...     raise KeyboardInterrupt
  ... finally:
  ...     print 'Goodbye, world!'
  ...
  Goodbye, world!
  KeyboardInterrupt
  

  Here’s another example:

  >>> def divide(x, y):
  ...     try:
  ...         result = x / y
  ...     except ZeroDivisionError:
  ...         print "division by zero!"
  ...     else:
  ...         print "result is", result
  ...     finally:
  ...         print "executing finally clause"
  ...
  >>> divide(2, 1)
  result is 2
  executing finally clause
  >>> divide(2, 0)
  division by zero!
  executing finally clause
  >>> divide("2", "1")
  executing finally clause
  Traceback (most recent call last):
    File "<stdin>", line 1, in ?
    File "<stdin>", line 3, in divide
  TypeError: unsupported operand type(s) for /: 'str' and 'str'
  

• The finally clause is indented to define clean-up actions.

  For example, if you opened a file and an exception was raised after opening it, you always want to close the file.

  The finally clause is especially useful when you want to release external resources.

Previous | Next