"Steven Bethard" wrote:
> John Reese wrote:
> > I now do:
> >
> > if isinstance(x, list):
> >
> > It is my understanding that this is what people do nowadays.
>
> I wouldn't go that far. I don't have an isinstance check for lists
> anywhere in my entire codebase. Why do you think you need to check to
> see if something is of type list? Why don't you just use it as needed,
> and find out, e.g.:
>
> try:
> itr = iter(x)
> except TypeError:
> # do whatever you need to do if it's not iterable
> else:
> # do whatever you need to do if it *is* iterable
A class of cases I've found necessary to do explicit type checking is
when a different action is taken for different types, but where duck
typing can't distinguish between them. For example, a function that
returns a string representation of an S-expression, represented as a
list of nested lists:
def s_expr(obj):
if isinstance(obj, list):
return "(%s)" % ' '.join(map(s_expr,obj))
else:
return str(obj)
>>> s_expr([1, [2,3], [4,5], "foo"])
>>> '(1 (2 3) (4 5) foo)'
Here duck typing doesn't help because the function should take the if
branch only for lists and not other iterables (e.g. strings).
George
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