Thoughts on using isinstance

[Maxim Sloyko]

On Jan 24, 3:38 pm, "abcd" <codecr... at gmail.com> wrote:
> In my code I am debating whether or not to validate the types of data
> being passed to my functions.  For example
>
> def sayHello(self, name):
>     if not name:
>         rasie "name can't be null"
>     if not isinstance(name, str):
>         raise "name must be a string"
>     print "Hello " + name
>
> Is the use of isinstance a "bad" way of doing things?  is it a "heavy"
> operation?  for example, if I use this in each function validate input
> will it slow things down a lot?
>
> just curious how you might handle this type of situation (other than
> not validating at all).
>
> thanks

My opinion is that validation is generally good.  However, you have to
make it not too strict.
For example, instead of

print "Hello " + name

you could have written

print "Hello " + str(name)

In this case requirement isinstance() will be too strict. The only
thing you have to check is that hasattr(name, "__str__")  and
callable(name.__str__)

In this case you can have validation, while at the same time enjoy full
flexibility of dynamic typing.

--
Maxim