Printing classes in Python with multiple values

Question

I have spent a good while searching through this website so I hope this question hasn't been asked before - apologises if it has. I'm learning classes for the first time and I'm making a class with multiple users (could be 50+ but for now, I just have 2 in my example). What I'm trying to do is have certain information about users/employees and be able to print them all in one go... in a way that isn't a complete eyesore! This is what I have attempted:

class User:

    def __init__(self, user_id, first, last, address):
        self.user_id = user_id
        self.first = first
        self.last = last
        self.address = address
        self.email = first + '.' + last + '@python.com'

    def all_users(self):
        print()
        print('User ID: {} First Name: {} {} {} {}'.format(self.user_id, self.first, self.last, self.address, self.email))
        print()


user_1 = User(123, 'Kim', 'N', 'London')

user_2 = User(312, 'Chris', 'E', 'Japan')

print(all_users(User))

This is the error message that I am receiving:

print('User ID: {} First Name: {} {} {} {}'.format(self.user_id, self.first, self.last, self.address, self.email))
AttributeError: type object 'User' has no attribute 'user_id'

Thanks in advance for any help or guidance.

User is a class, not an object. You've confused the two in your program. user_1 and user_2 have the attributes; User does not. — Prune
– Prune, Commented Apr 6, 2018 at 18:05
@Prune well, classes are objects :) But I think fundamentally the OP is under the misapprehension that classes automatically act as containers for instances of themselves. — juanpa.arrivillaga
– juanpa.arrivillaga, Commented Apr 6, 2018 at 18:12
all_users() is a very misleading method name, as it only prints information for one user. — John Gordon
– John Gordon, Commented Apr 6, 2018 at 18:16

John Gordon · Accepted Answer · 2018-04-06 18:42:18Z

3

Sounds like you want the User class to contain a list of all users.

This is called a class variable because it is attached to the class itself, instead of being attached to a particular instance of the class.

Example code:

class User(object):

    users = []

    def __init__(self, first, last):
        self.first = first
        self.last = last

        # now that this instance is fully initialized, add it
        # to the master list of users
        User.users.append(self)

    def __str__(self):
        return '{} {}'.format(self.first, self.last)

    @staticmethod
    def all_users():
        for user in User.users:
            print (user)

user_1 = User('Kim', 'Smith')
user_2 = User('Chris', 'Jones')

User.all_users()

answered Apr 6, 2018 at 18:42

John Gordon

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2 Comments

progmatico Over a year ago

This is a good alternative to defining a container class or using a list. The class can keep a list of its own instances.

Mandy Boo Over a year ago

Brilliant John Gordon - that makes sense. I'm still learning in my own time but it is great to have a place like this to come to get help when stuck. Thanks to everyone for their assistance and time.

Brendan Abel · Accepted Answer · 2018-04-06 18:22:14Z

3

You should probably implement the __str__ or __repr__ special methods, which are designed to print human readable and "official" representations of the class instances, respectively

class User():
    ...

    def __str__(self):
        attrs = ['{}={}'.format(k, repr(v)) for k, v in self.__dict__.items()]
        return '{}({})'.format(self.__class__.__name__, ', '.join(attrs))

Then it would look like this

>>> user = User('123', 'John', 'Doe', 'USA')
>>> print(user)
User(user_id='123', first='John', last='Doe', address='USA', email='[email protected]')

edited Apr 6, 2018 at 18:22

answered Apr 6, 2018 at 18:16

Brendan Abel

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