Some questions regarding classes

[snippsat]

1. why in class Pets it is necessary to open an empty list

Can just delete has no function(yet) other than it's a empty list that belong to the class,the output will be same.
You can look at list at bye calling it with class name.

I have 3 dogs.
Tom is 6
Fletcher is 7
Larry is 9
And they're all mammals, of course.

# Call it
>>> Pets.dogs
[]

# The instance attributes has the same name "dogs",but it don't overwrite the class attribute dogs
>>> my_pets.dogs
[<__main__.Bulldog object at 0x03B2AE30>,
 <__main__.RussellTerrier object at 0x03B2AE70>,
 <__main__.Dog object at 0x03B2ADF0>]
>>> 

2. this line confuses me:
Python Code: (Double-click to select all)

print(f'I have {len(my_pets.dogs)} dogs.')

why my_pets.dogs? I don't see a connection. dogs is attribute of the class Pet. Does dogs represents names in my_dogs list methods?

It just used to count,so in the list there will be 3 new instances.

>>> my_pets.dogs
[<__main__.Bulldog object at 0x03B2AE70>,
 <__main__.RussellTerrier object at 0x03B2ADF0>,
 <__main__.Dog object at 0x03B2AD50>]

>>> len(my_pets.dogs)
3

# In the loop this happens when methods get called 
>>> my_pets.dogs[0].name
'Tom'
>>> my_pets.dogs[0].age
6

what is dog?

See if output is the same

for dog in my_pets.dogs:
    print(f'{dog.name} is {dog.age}')

# Try
for rubberduck in my_pets.dogs:
    print(f'{rubberduck.name} is {rubberduck.age}')