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

Michael Urman murman at gmail.com
Mon Jun 26 15:15:08 CEST 2006

On 6/25/06, Raymond Hettinger <raymond.hettinger at verizon.net> wrote:

Those were not empty words. I provided two non-trivial worked-out examples taken from sreconstants.py and opcode.py. Nick provided a third example from decimal.py. In all three cases, the proposal was applied effortlessly resulting in improved readability and speed. I hope you hold other proposals to the same standard.

I appreciate your attempts to help us avoid overengineering this so I'm trying to find some real world examples of a pygame event loop that really show the benefit of supporting named constants and expressions. I may mess up irrelevant details, but the primary case looks something like the following (perhaps Pete Shinners could point us to a good example loop online somewhere):

for event in pygame.event.get():
    if event.type == pygame.KEYDOWN: ...
    elif event.type == pygame.KEYUP: ...
    elif event.type == pygame.QUIT: ...

Here all the event types are integers, but are clearly meaningless as integers instead of an enumeration. I'd be sorely disappointed with the addition of a switch statement that couldn't support this as something like the following:

for event in pygame.event.get():
    switch event.type:
    case pygame.KEYDOWN: ...
    case pygame.KEYUP: ...
    case pygame.QUIT: ...

I'd also generally like these to be captured like default values to function arguments are. The only argument against this that stuck with me is over the fact that locals cannot be used. If literals-only has a chance, than I would hope that every hashable non-local capturable expression should be at least as welcome. In summary I'm +0 on switch, but -1 on literal-only cases.

I also would like to see a way to use 'is' instead of (or inaddition to) '==' for the comparison, but I don't have any use cases behind this.

Michael

Michael Urman http://www.tortall.net/mu/blog

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