Python中的枚举：isInstance错误

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

Answer 1

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.

Answer 2

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

Answer 3

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