What is the intended use of the optional else
clause of the try
statement?
The statements in the else
block are executed if execution falls off the bottom of the try
- if there was no exception. Honestly, I've never found a need.
However, Handling Exceptions notes:
The use of the else clause is better than adding additional code to the try clause because it avoids accidentally catching an exception that wasn’t raised by the code being protected by the try ... except statement.
So, if you have a method that could, for example, throw an IOError
, and you want to catch exceptions it raises, but there's something else you want to do if the first operation succeeds, and you don't want to catch an IOError from that operation, you might write something like this:
try:
operation_that_can_throw_ioerror()
except IOError:
handle_the_exception_somehow()
else:
# we don't want to catch the IOError if it's raised
another_operation_that_can_throw_ioerror()
finally:
something_we_always_need_to_do()
If you just put another_operation_that_can_throw_ioerror()
after operation_that_can_throw_ioerror
, the except
would catch the second call's errors. And if you put it after the whole try
block, it'll always be run, and not until after the finally
. The else
lets you make sure
finally
block, andIOError
s it raises aren't caught here