Need instruction on how to use isinstance

[Stephen Hansen]

On 6/27/10 7:09 PM, Steven W. Orr wrote:
> So, my question is, what value can I use as the 2nd arg to isinstance to see if
> foo is a function? And while I'm on the subject, what types does isinstance not
> support?

Does it have to be a function? -- There's quite a few things which are 
function-y enough that you really should accept them even if they may 
not be technically a /function/. Like a class instance with the __call__ 
method defined wrapping a function as a decorator. Or a bound method, 
really.

In Python 2.x, you can use callable(fun) -- that goes away in Py3 
though. But personally, I think this is the wrong approach.

I'm assuming you need to do some different sort of behavior based on if 
its a str, tuple or list-- okay.

But, personally-- at that point, I would just *assume* the argument is a 
function. And call it.

If it can't be called, its not a functiony-thing. You can either let 
that traceback propagate, or just raise a TypeError "expected arg to be 
a string, tuple, list or callable".

Then again, similarly I almost never want to test for if somethings a 
tuple or list. I'd rather use it as a sequence type and see if it works: 
while there's not as many 'sequency-like-things' out there as there are 
function-like-things, there's still quite a few.

So personally, I'd check if its a string (can it be unicode or regular? 
If so isinstance(x,basestring)).

Then I'd try to use it as a sequence, doing whatever I woulda done with 
it sequence-like. If that works, great. If not, I'd try to call it.

Etc.

Then again it does depend on just what you're *doing* with the arg being 
passed in.

-- 

    ... Stephen Hansen
    ... Also: Ixokai
    ... Mail: me+list/python (AT) ixokai (DOT) io
    ... Blog: http://meh.ixokai.io/