Enums in Python: isInstance error

Question

What is wrong with this code and is that implementation correct?

from enum import Enum

class Test(object):
    Filters = Enum('Filters', 'A B C')  
    def __init__(self):
        pass

    def aaa(self, filters):
        if(isinstance(filters, self.Filters.B)):
            print 'OK'
        else:
            print 'NOT OK'
if __name__ == '__main__':
    Test().aaa(Test.Filters.B)

Error is:

Traceback (most recent call last):
  File "test.py", line 14, in <module>
    Test().aaa(Test.Filters.B)
  File "test.py", line 9, in aaa
    if(isinstance(filters, Test.Filters.B)):
TypeError: isinstance() arg 2 must be a type or tuple of types

Have you tried to execute it? if no, whats the error message? — Serbitar
– Serbitar, Commented Feb 19, 2016 at 10:48

Ethan Furman · Accepted Answer · 2016-02-19 17:45:45Z

3

If you want to know if the filters parameter is a member of the Test.Filters Enum, you have three choices

isinstance(filters, Test.Filters)
filters in self.Filters

(Test and self are interchangeable.)

If you want to know if the filters parameter is Test.Filters.B then a simple comparison will work:

filters is self.Filters.B

answered Feb 19, 2016 at 17:45

Ethan Furman

70.1k21 gold badges174 silver badges251 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Alaa M. Over a year ago

Used this for IronPython: filters in self.Filter

tobias_k · Accepted Answer · 2016-02-19 10:53:01Z

2

The error you get is quite clear:

TypeError: isinstance() arg 2 must be a type or tuple of types

Filters.B is not a class or type. Instead of using isinstance, just compare the value that you got with the one you want:

if filters is Test.Filters.B:

Also, Filters is an attribute of the class, not of the instance, so you should probably rather use Test.Filters, although self.Filters seems to work, too.

answered Feb 19, 2016 at 10:53

tobias_k

83.1k12 gold badges130 silver badges186 bronze badges

Comments

Serbitar · Accepted Answer · 2016-02-19 11:13:29Z

-1

self.Filters.B

is not defined. You defined

Filters.B

Also:

self.Filters.B

needs to be:

type(self.Filters.B)

it works like this:

class A():
    pass

isinstance(3, int) == True
isinstance(3,type(4)) == True
isinstance("hello", type('something')) == True
isinstance("hello", str) == true
isinstance(A(), type(A())) == True
isinstance(A(), A) == True

edited Feb 19, 2016 at 11:13

answered Feb 19, 2016 at 10:49

Serbitar

2,22422 silver badges26 bronze badges

6 Comments

tobias_k Over a year ago

Nope, that's not the problem.

Me Like Cookies Over a year ago

i don't get it. How to fix it, or even better. How should that be made correctly?

tobias_k Over a year ago

Note that using if isinstance(filters, type(self.Filters.B)) (or whatever exactly you did, it's not really clear from the answer) will only check whether filters is a Filter, not whether it's Filter.B. Try passing Fitler.A as parameter.

tobias_k Over a year ago

isinstance(A(), type(A)) == True wrong! type(A) is type. You can do either isinstance(A(), A) or type(A()) == A, but isinstance(A(), type(A)) won't work.

Me Like Cookies Over a year ago

THANKS guys for all the help and details! You are awesome! I've finally got that!

|

Collectives™ on Stack Overflow

Enums in Python: isInstance error

3 Answers 3

1 Comment

Comments

6 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

6 Comments

Your Answer

Sign up or log in

Post as a guest

Related