Python inheritance from lists [duplicate]

Question

This question already has answers here:

Understanding Python super() with __init__() methods [duplicate] (7 answers)

Closed 9 years ago.

I just started learning Python, and created the following class, that inherits from list:

class Person(list):
 def __init__(self, a_name, a_dob=None, a_books=[]):
 #person initialization code
 list.__init__(a_books)
 self.name = a_name
 self.dob = a_dob

However, there are three things I don't understand:

1. This line list.__init__(a_books), doesn't actually initialize my instance's list of books.
2. I am supposed, according to the book, write list.__init__([]) instead. Why is this step necessary.
3. Why is there no reference to self in list.__init__([])? How does Python know?

• Penguin Brian: For a practical system you probably want list to be an attribute of Person rather then inherit from list.

Answer 1

You need to make a super call to instantiate the object using the parents __init__ method first:

class Person(list):
 def __init__(self, a_name, a_dob=None, a_books=[]):
 #person initialization code
 super(Person, self).__init__(a_books)
 self.name = a_name
 self.dob = a_dob
print Person('bob',a_books=['how to bob'])

Gives the output:

['how to bob']

Because list has a __str__ method.