CODEWITHSUNDEEP
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Reputation: 103

Enums in Python: isInstance error

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

Upvotes: 2

Views: 3421

Answers (3)

Ethan Furman
Ethan Furman

Reputation: 69021

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

Upvotes: 3

Serbitar
Serbitar

Reputation: 2224

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

Upvotes: -1

tobias_k
tobias_k

Reputation: 82889

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.

Upvotes: 2

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