How to compare inheritance with several classes?

Question

I want to check if an object is an instance of any class in a list/group of Classes, but I can't find if there is even a pythonic way of doing so without doing

if isinstance(obj, Class1) or isinstance(obj, Class2) ... or isinstance(obj, ClassN):
    # proceed with some logic

I mean, comparing class by class.

It would be more likely to use some function similar to isinstance that would receive n number of Classes to compare against if that even exists.

Thanks in advance for your help!! :)

How can it be that `help(isinstance)` is harder than taking the time to post to SO? o_0 — rantanplan, May 05 '12 at 01:55
It is worth noting that checking type/class is [generally discouraged](http://stackoverflow.com/questions/1549801/differences-between-isinstance-and-type-in-python). Duck-typing and `try`/`except` is considered a better practice. — yentsun, May 05 '12 at 02:56

score 31 · Accepted Answer · answered May 05 '12 at 01:45

You can pass a tuple of classes as 2nd argument to isinstance.

>>> isinstance(u'hello', (basestring, str, unicode))
True

Looking up the docstring would have also told you that though ;)

>>> help(isinstance)
Help on built-in function isinstance in module __builtin__:

isinstance(...)
    isinstance(object, class-or-type-or-tuple) -> bool

    Return whether an object is an instance of a class or of a subclass thereof.
    With a type as second argument, return whether that is the object's type.
    The form using a tuple, isinstance(x, (A, B, ...)), is a shortcut for
    isinstance(x, A) or isinstance(x, B) or ... (etc.).

What about `isinstance(x,A) and isinstance(x,B)`? Is there an easy way to do that? — Allen Wang, Aug 03 '17 at 14:24

score 2 · Answer 2 · answered May 05 '12 at 01:47

isinstance(obj, (Class1, Class2, ..., ClassN)), or isinstance(obj, BaseClass) if they have a common ancestor.

That said, you should think twice before using this. Explicit type checking like this can hurt genericity of the code, so you'd better have a reason for throwing duck typing away.

yentsun · Answer 3 · 2012-05-05T02:02:04.733

-1

Another way to do it, though without subclass check:

>>> obj = Class2()
>>> type(obj) in (Class1, Class2, Class3)
True

Note. Probably this is just for taking into consideration, not for practical use.

edited May 05 '12 at 02:02

answered May 05 '12 at 01:55

yentsun

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Not the same. It won't consider subclasses like `isinstance`. – Cat Plus Plus May 05 '12 at 01:57
@CatPlusPlus I'll make a note on that – yentsun May 05 '12 at 02:01
1

@yentsun Also it doesn't play well with old style classes. `class A: pass` and `class B: pass` instances will have the same type of `` and fail that test. – krousey May 05 '12 at 02:08

How to compare inheritance with several classes?

3 Answers3