Cannot change class members value after final assert statements

Given I have a test class with two or more test functions, and the class has class members who are assigned static strings from a config file, When I reassign one of the class members value after the assert statement in the first test function (regardless whether this is the first function in the test or one before last), Then in the following test the class member remains with the value that was assigned to it, prior to the change.

pytest 3.6.1

class MyTest():
    a = "dog"
    b = "cat"
    
    def test_one(self):
        assert 1 + 1 == 2
        self.a = self.b

    def test_two(self):
        # here self.a is equal to "dog" instead of "cat"

[RonnyPfannschmidt]

each test gets a new instance, as far as pytest is concerned this is a feature

[MosheSheena]

Thank you @LaurentMarchelli for this clear example! I will certainly adopt this.