Student.name = ''
Student.set_score = set_score

class Student():
__slots__ = ('name', 'age')

S1 = Student()
S1.name = 'Jack' # ok!
S1.score = 123 # error!

> class Student(object):
... pass
... 
> Abey = Student()
> Abey.name = 'Abey'
> Abey.__dict__
{'name': 'Abey'}

> class Student(object):
... __slots__ = ('name', 'age')
... 
> Abey = Student()
> Abey.name = 'Abey'
> Abey.gender = 'Female'
Traceback (most recent call last):
 File "<input>", line 1, in <module>
AttributeError: 'Student' object has no attribute 'gender'
> Abey.__dict__
Traceback (most recent call last):
 File "<input>", line 1, in <module>
AttributeError: 'Student' object has no attribute '__dict__'

> class Student(object):
... __slots__ = ('name', 'age')
... 

> class SubStudent(Student):
... pass
... 
> Bob = SubStudent()
> Bob.gender = 'Male'
> Bob.__dict__
{'gender': 'Male'}

> class SubStudent2(Student):
... __slots__ = 'gender'
... 
> Cathy = SubStudent2()
> Cathy.gender = 'Female'
> Cathy.name = 'Cathy'
> Cathy.teacher = 'Mrs. Wang'
Traceback (most recent call last):
 File "<input>", line 1, in <module>
AttributeError: 'SubStudent2' object has no attribute 'teacher'

> class SubStudent3(Student):
... __slots__ = ('name', 'age', 'gender')
... 
> from sys import getsizeof
> getsizeof(Student()), getsizeof(SubStudent2()), getsizeof(SubStudent3())
(56, 64, 80)

import timeit

class Foo(object): __slots__ = 'foo',

class Bar(object): pass

slotted = Foo()
not_slotted = Bar()

def get_set_delete_fn(obj):
 def get_set_delete():
 obj.foo = 'foo'
 obj.foo
 del obj.foo
 return get_set_delete

> 0.3664822799983085 / 0.2846834529991611
1.2873325658284342