从Python中的buitin类继承

Question

How does johny gets the functionality of list even if the third line in the code is commented, as it is the initialisation?So then what is the significance of that line?

class Namedlist(list):
    def __init__(self,name):
          list.__init__([])  #This line even if commented does not affect the output
          self.name=name

johny=Namedlist(john)
johny.append("artist")
print(johny.name)
print(johny)

>>john
>>artist

Answer 1

The line in your code list.__init__([]) does nothing because you if you want to modify the object you are instantiating, you need to call super() not the list built-in (or use list.__init__(self, []) , but that seems more confusing to me).

The call to super().__init__() is usefull to pass along initial data for the list, for example.

I suggest you change your code to this:

class NamedList(list):
    def __init__(self, name, *args, **kwargs):
          # pass any other arguments to the parent '__init__()'
          super().__init__(*args, **kwargs)

          self.name = name

To be user like this:

>>> a = NamedList('Agnes', [2, 3, 4, 5])
>>> a.name
'Agnes'
>>> a
[2, 3, 4, 5]

>>> b = NamedList('Bob')
>>> b.name
'Bob'
>>> b
[]
>>> b.append('no')
>>> b.append('name')
>>> b
['no', 'name']

Any iterable works as initial data, not just lists:

>>> c = NamedList('Carl', 'Carl')
>>> c.name
'Carl'
>>> c
['C', 'a', 'r', 'l']