At Wednesday 24/1/2007 14:21, abcd wrote:
>Yes because usually you don't expect a list or dictionary but some object
> that *acts* like a list or dictionary. Or you even expect just some
> aspects of the type's behavior. For example that it is something you can
> iterate over.
>
> Ciao,
> Marc 'BlackJack' Rintsch
good point. is there place that documents what methods/attrs I should
check for on an object? for example, if its a list that I expect I
should verify the object that is passed in has a ??? function? etc.
Don't insist on checking! :)
Just try to use the object - you'll get an exception at first invalid usage.
By example, a lot of functions take a file parameter to output
something on it. Usually the *only* method called is write(). So any
object with a write() method (taking a single string argument) would
be fine; StringIO are an example. Checking if the argument is an
instance of the file type would make that impossible.
Anyway, sometimes it's ok to check in advance - but please consider
to check the *behavior* you expect, not the exact instance type. In
the example above, you can validate that fileobject has a write
attribute: getattr(fileobject, "write"). But I'd only do that if I
have a good reason (perhaps if the file is used after some lengthy
calculation,and I want to be sure that I will be able to store the result)
--
Gabriel Genellina
Softlab SRL
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