[Python-Dev] Switch statement (original) (raw)

BJörn Lindqvist bjourne at gmail.com
Mon Jun 26 03:10:22 CEST 2006

On 6/23/06, Edward C. Jones <edcjones at comcast.net> wrote:

Python is a beautiful simple language with a rich standard library. Python has done fine without a switch statement up to now. Guido left it out of the original language for some reason (my guess is simplicity). Why is it needed now? What would be added next: do while or goto? The urge to add syntax should be resisted unless there is a high payoff (such as yield).

There are much better ways for the developers to spend their time and energy (refactoring os comes to mind). Please keep Python simple. -1 on the switch statement.

I agree. IMHO switch is a useless statement which can cause many problems in any language. It misleads programmers to dispatch in the wrong way. If you have switch with < 5 cases, an if-elif chain fits just fine. If the switch is larger use a dictionary that maps values to functions. In C, many times a switch block starts small (40 lines) but grows as the number of values to dispatch on increases. Soon it becomes a 500 line monstrosity that is impossible to refactor because variables from the enclosing space is used frivolously.

I don't get the speed argument either. Who cares that if-elif-chains are O(n) and switch O(1)? If n > 10 you are doing something wrong anyway. I don't think I have ever seen in any language a switch construct that, barring speed concerns, wouldn't be better written using any other dispatch mechanism than switch.

-- mvh Björn

More information about the Python-Dev mailing list