> GvR> if isinstance(x, str) or isinstance(x, unicode): > > is
> GvR> apparently too much typing.
>
> NS> Perhaps we could extend isinstance(). How about
>
> NS> isinstance(x, str, unicode)
>
> NS> or
>
> NS> isinstance(x, (str, unicode))
>
> NS> This is a common problem not limited to string types. I often
> NS> want to test if something is a tuple or a list for example.
>
> That's an interesting idea, but please use the former signature, not
> the latter.
Why? The varargs signature makes it less convenient (and less
efficient!) to pre-calculate the list of types. It also makes it
harder to implement this in PyObject_IsInstance(), so that C code can
use this convenience. Finally, if I already know the meaning of
isinstance(x, y), then when I encounter isinstance(x, (y, z)) for the
first time, it's very easy to guess the meaning. The meaning of
isinstance(x, y, z) is much more murky: z could be an optional
argument specifying some other modification of the basic isinstance().
> And what would it return? It needs to return a true value on success,
> but maybe instead of returning 1, it might be more useful to return
> the type argument that matched, e.g.:
>
> >>> isinstance('', str, unicode)
> <type 'str'>
> >>> isinstance(u'', str, unicode)
> <type 'unicode'>
> >>> isinstance((), list, dictionary, tuple)
> <type 'tuple'>
> >>> isinstance(7, list, dictionary, tuple)
> 0
Here I agree with Fred: too much hackery combined in one function.
And what's the use case?
--Guido van Rossum (home page: http://www.python.org/~guido/)
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