init method of a class

See “Class instantiation” in Class Objects. The __init__ method of class has two underscores in front and two in back. That’s because __init__ is a special method.

"""
Create a class named Person.  Then instantiate this class several times,
i.e., create several instantiations (objects) of this class.
"""

import sys

class Person(object):   #The (object) is unnecessary: you get it anyway.
    "Class Person demonstrates the __init__method and 3 instance attributes."

    def __init__(self, lastName, age, favoriteSongs = None):
        "If the arguments are valid, instantiate a Person object."
        if not isinstance(lastName, str):
            raise TypeError("lastName must be a str")
        if lastName == "":
            raise ValueError("lastName must not be empty")

        if not isinstance(age, (int, float)):
            raise TypeError("age must be int or float")
        if age < 0 or age > 120:
            raise ValueError("age must be in the range 0 to 120 inclusive")

        if not isinstance(favoriteSongs, list) and favoriteSongs is not None:
            raise TypeError("favoriteSongs must be list or None")

        self.lastName = lastName
        self.age = age
        self.favoriteSongs = favoriteSongs


#Create one instance of class Person:

try:
    mark = Person("Meretzky", 64, ["Help!", "Day Tripper", "Piggies"])
except BaseException as error:
    print(error, file = sys.stderr)
    sys.exit(1)

print(f'mark.lastName = "{mark.lastName}"')
print(f"mark.age = {mark.age}")
print(f"mark.favoriteSongs = {mark.favoriteSongs}")
print()

#Mass produce many instances of class Person.  Store them in a list.

students = [
    ["Chan",     10],
    ["Cooper",   20],
    ["Franklin", 30],
    ["Hsu",      40],
    ["Leyl",     50],
    ["Phu",      60],
    ["Rutledge", 70]
]

lengths = [len(student[0]) for student in students]      #Each student is a list containing 2 items.
maxLength = max(lengths)

try:
    persons = [Person(*student) for student in students] #Each student is a list containing 2 items.
except BaseException as error:
    print(error, file = sys.stderr)
    sys.exit(1)

for person in persons:
    print(f"{person.lastName:{maxLength}} {person.age:3}")

sys.exit(0)

mark.lastName = "Meretzky"
mark.age = 64
mark.favoriteSongs = ['Help!', 'Day Tripper', 'Piggies']

Chan      10
Cooper    20
Franklin  30
Hsu       40
Leyl      50
Phu       60
Rutledge  70

Things to try

What happens if you give a bad argument to __init__?

Have __init__ raise a TypeError if favoriteSongs contains an item that is not a string. I hope every bool in the following listOfBools is True.

        if favoriteSongs is not None:
            if not isinstance(favoriteSongs, list):
                raise TypeError("favoriteSongs must be list or None")
            listOfBools = [isinstance(song, str) for song in favoriteSongs]
            if not all(listOfBools):
                raise TypeError("Every song must be a str")

__init__ method of a class

Things to try

init method of a class