An example showcasing the need for developer friendly messages

Medium.py

class Medium(object):

    def __init__(self, username, age, interests):
        self.username = username
        self.age = age
        self.interal_id=2939
        self.interests = interests
    
    def __str__(self):
        '''
        We swap the default string output of this class with an informative
        description of the properties of this Medium object, including the user
        handle, their age, and their interests.
        '''
        return "Medium user: @{0}; age: {1}; interests: {2}" \
                    .format(self.username, self.age, ', '.join(map(str, self.interests)))
        
    def __repr__(self):
        '''
        This is a developer-friendly message: let's print the internal id of this user,
        and how many interests they have on file.
        '''
        return "user id={0},interests_count={1}".format(self.interal_id, len(self.interests))


me = Medium("ahmedsakr", 23, ['philosophy', 'programming', 'netflix'])
# output: Medium user: @ahmedsakr; age: 23; interests: philosophy, programming, netflix
print (me)

# output: user id=2939,interests_count=3
print (repr(me))