Python isinstance（var，Type）总是返回False

Question

I'm using Django with Python3. There's a class defined in Model:

class PeopleAround(models.Model):
    aaa_Id = models.ForeignKey(Board)
    bbb = models.CharField(max_length=40)
    ccc_Id = models.CharField(max_length=20)
    ddd_Id = models.CharField(max_length=20)

in a view, I'm successfully retrieved some data by following:

peopleAroundInDb = PeopleAround.objects.filter(aaa_Id=0).all()

and when do a testing, what surprised me is the expression below always return False:

isinstance(peopleAroundInDb[0], models.PeopleAround.__class__)

and also tested with equality for:

id(PeopleAround.__class__) and id(type(peopleAroundInDb[0]))

also NOT equal.

so anyone could help?

Answer 1

Don't use __class__ - as this returns a type object.

Just do this:

isinstance(peopleAroundInDb[0], models.PeopleAround)

Example:

>>> isinstance('text', str.__class__)
False
>>> isinstance('text', str)
True

Python doesn't need the class type object to compare, it wants to compare to the class itself.

EDIT:

This technically works:

>>> class test:
...     def blah(self, thing):
...         print(isinstance(thing, self.__class__))
...         print(isinstance(thing, test))
...
>>> a = test()
>>> b = test()
>>> a.blah(b)
True
True

But I would say that it is clearer, and therefore a better idea, to use isinstance(thing, test) over isinstance(thing, self.__class__)