[Baypiggies] Newbie-ish type questions...

[Chad Netzer]

On Wed, Apr 23, 2008 at 9:29 AM, Paul McNett <p at ulmcnett.com> wrote:
> Kelly Yancey wrote:
>
> > But, yes, it gets better in 3.0:
> >    http://www.python.org/dev/peps/pep-3119/
> >
>
>  Now *that* is reason alone to migrate to 3.0.
>
>  def myfunc(seq=None):
>   if seq is None:
>     seq = ()
>   assert isinstance(seq, Sequence)

And in the meantime, it illustates that (generally) you should test
for behaviors, not type.  The 'operator' module has some useful
predicates:

isSequenceType()
isNumberType()
isMappingType()

So the assertion above becomes:

assert operator.isSequenceType(seq)

If you need a sequence to be a list, just convert it:

seq = list(seq)

With these tools, you should almost never use "type(a) is list", or
similar, in your code.

* Note - I have no idea how isSequenceType() deals with iterators or
generators...  Does someone have a few moments to test this?