Question about isinstance()

Magnus Lycka lycka at
Fri Jan 27 08:16:47 EST 2006

Mr.Rech wrote:
> Hi all,
> I've read some thread about isinstance(), why it is considered harmful
> and how you can achieve the same results using a coding style that
> doesn't break polymorphism etc... Since I'm trying to improve my Python
> knowledge, and I'm going to design a class hierarchy from scratch, I'd
> like to have some feedback about this from those of you much more
> experienced than me in OOP.
> Any better way to write this method? Any suggestion?

It's really impossible to tell what's good Python code
based on details like this. isinstance() wouldn't be in
Python if you weren't supposed to use it, but you need to
understand when you should limit your functions to work
with a specific kind of data, and when you should try to
be broader. This is a design decision that will influence
the usability and maintainability of your code. We can't
help you figure out how to make such trade-offs based on
your implementation of __eq__.

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