On 4/25/05, M.-A. Lemburg <[EMAIL PROTECTED]> wrote: > Shannon -jj Behrens wrote: > > On 4/20/05, M.-A. Lemburg <[EMAIL PROTECTED]> wrote: > > > >>Fredrik Lundh wrote: > >> > >>>PS. a side effect of the for-in pattern is that I'm beginning to feel > >>>that Python > >>>might need a nice "switch" statement based on dictionary lookups, so I can > >>>replace multiple callbacks with a single loop body, without writing too > >>>many > >>>if/elif clauses. > >> > >>PEP 275 anyone ? (http://www.python.org/peps/pep-0275.html) > >> > >>My use case for switch is that of a parser switching on tokens. > >> > >>mxTextTools applications would greatly benefit from being able > >>to branch on tokens quickly. Currently, there's only callbacks, > >>dict-to-method branching or long if-elif-elif-...-elif-else. > > > > I think "match" from Ocaml would be a much nicer addition to Python > > than "switch" from C. > > PEP 275 is about branching based on dictionary lookups which > is somewhat different than pattern matching - for which we > already have lots and lots of different tools. > > The motivation behind the switch statement idea is that of > interpreting the multi-state outcome of some analysis that > you perform on data. The main benefit is avoiding Python > function calls which are very slow compared to branching to > inlined Python code. > > Having a simple switch statement > would enable writing very fast parsers in Python - > you'd let one of the existing tokenizers such as mxTextTools, > re or one of the xml libs create the token input data > and then work on the result using a switch statement. > > Instead of having one function call per token, you'd > only have a single dict lookup. > > BTW, has anyone in this thread actually read the PEP 275 ?
I'll admit that I haven't because dict-based lookups aren't as interesting to me as an Ocaml-style match statement. Furthermore, the argument "Instead of having one function call per token, you'd only have a single dict lookup" isn't very compelling to me personally, because I don't have such a performance problem in my applications, which isn't to say that it isn't important or that you don't have a valid point. Best Regards, -jj -- I have decided to switch to Gmail, but messages to my Yahoo account will still get through. _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
