typechecks: just say no! (was Re: Determining Types)

[Marcin 'Qrczak' Kowalczyk]

Mon, 03 Sep 2001 14:31:04 GMT, David C. Ullrich <ullrich at math.okstate.edu> pisze:

> In yet other places I want to iterate over the fields 
> of a record, as in
> 
> for key, value in rec:
> 
> So in __getitem__ I check the type of index, returning
> getattr(self, index) if index is a string and saying
> 
> fieldname=self.__fieldnames__[index]
> return (fieldname, getattr(self, fieldname))
> 
> if index is an integer.

Newer versions of Python allow to define how the object is iterated over
independently of indexing.

Define method __iter__ which returns an iterator (an object which
keeps a state, whose next method returns the next object or raises
StopIteration, and whose __iter__ method returns self).

In this case the iterator can be defined thus (untested):

    def __iter__(self):
        for name in self.__fieldnames__:
            yield (name, getattr(self, name))

You will need
    from __future__ import generators
at the top of the module.

BTW, iteration over a dictionary now yields its keys. You may consider
conforming to this convention:

    def __iter__(self):
        return iter(self.__fieldnames__)

-- 
 __("<  Marcin Kowalczyk * qrczak at knm.org.pl http://qrczak.ids.net.pl/
 \__/
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QRCZAK