How to set and get a parent class attribute from an inherited class in Python?

Question

I have the Family and its inherited Person classes. How do I get the familyName attribute from the Person class?

class Family(object):
    def __init__(self, familyName):
        self.familyName = familyName

class Person(Family):
    def __init__(self, personName):
        self.personName = personName

For instance, let these Family and Person objects:

strauss = Family('Strauss')
johaness = Person('Johaness')
richard = Person('Richard')

I'd like to do something such as:

print richard.familyName

and get 'Strauss'. How can I do this?

Answer 1

You cannot.

Instances only inherit the parent class methods and attributes, not instance attributes. You should not confuse the two.

strauss.familyName is an instance attribute of a Family instance. The Person instances would have their own copies of the familyName attribute.

You normally would code the Person constructor to take two arguments:

class Person(Family):     def __init__(self, personName, familyName):         super(Person, self).__init__(familyName)         self.personName = personName  johaness = Person('Johaness', 'Strauss') richard = Person('Richard', 'Strauss') 

An alternative approach would be for Person to hold a reference to a Family instance:

class Person(object):     def __init__(self, personName, family):         self.personName = personName         self.family = family 

where Person no longer inherits from Family. Use it like:

strauss = Family('Strauss') johaness = Person('Johaness', strauss) richard = Person('Richard', strauss)  print johaness.family.familyName 

Answer 2

In addition to Martijns suggestions, you can also create the Person from the Family instance, that way letting the family keep track of it's members:

class Person(object):     def __init__(self, person_name, family):         self.person_name = person_name         self.family = family      def __str__(self):         return ' '.join((self.person_name, self.family.family_name))  class Family(object):     def __init__(self, family_name):         self.family_name = family_name         self.members = []      def add_person(self, person_name):         person = Person(person_name, self)         self.members.append(person)         return person      def __str__(self):         return 'The %s family: ' % self.family_name + ', '.join(str(x) for x in self.members) 

Usage like this:

>>> strauss = Family('Strauss') >>> johannes = strauss.add_person('Johannes') >>> richard = strauss.add_person('Richard') >>>  >>> print johannes Johannes Strauss >>> print richard Richard Strauss >>> print strauss The Strauss family: Johannes Strauss, Richard Strauss