Adding Attributes to a Python Class

@Joseph Flanagan, agreed, it would have been better to use a == b in this case.

However, this is the kind of mistake that somehow still works. When a class does not define .__eq__(), == is essentially equal to is. More precisely:

User-defined classes have __eq__() and __hash__() methods by default; with them, all objects compare unequal (except with themselves)

(Source: docs.python.org/3/reference/datamodel.html#object.__hash__)

Great course! What about attributes that are defined out of the __init__()? Are they still instantiated when it is called eg class Person:

def __init__(self, name):
    self.name = name
    self.age= age
    self.astrosign = astrosign

Will the last two attributes be called when the init is called?

@henrytirla Attributes declared outside of .__init__() or any other method are attached to the enclosing class. They’re defined even before any instance of that class exists and are shared across all existing instances.

For example, consider this Person class:

>>> class Person:
... 
...     counter = 42
... 
...     def __init__(self, name):
...         self.name = name
...
>>> Person.counter  # There are no instances of this class yet
42
>>> alice = Person("Alice")
>>> bob = Person("Bob")
>>> alice.counter
42
>>> bob.counter
42

However, when you wish to change the value of a class attribute, you should always refer to it through the class name instead of a particular instance. Otherwise, unexpected things start to happen. You’re creating an instance attribute with the same name that masks the class attribute:

>>> alice.counter = 15  # Defines an instance attribute in Alice
>>> alice.counter
15
>>> bob.counter  # Bob has no such attribute
42
>>> Person.counter  # ...so, it delegates to the class attribute
42 

Would it be better to set the species in the __init__ function? For example, self.species = 'mammal'. I guess I’ve just never seen it done the way shown in the tutorial.

@chananya7276 “Better” is a highly subjective term because it all depends on the circumstances 😉 This lesson introduces the concept of class attributes, and species was defined as one for the sake of example.

Hey Austin, not able to understand the phrase at 03:56, “… we can use the access modifier, which in python is a dot(.)”. Aren’t access modifiers public, protected and private in general?

I am new to Python. If class attributes is what I understand is default, would changing it as per your example make sense?

Can I get clarification that a class attribute when changed by one instance, is changed for all instances?

The class variable is shared among all instances of a class, rather than being unique to each instance. It is called static variable in Java.

The first comment is from 2019. This video is a little stale. (Kind of like my Python skills.)

This is the print statement with f-strings:

print(f"{philo.name} is {philo.age} and {mikey.name} is {mikey.age}")