Why won't my python class inherit from another class?

Question

class Media_Work(object):

  def __init__(self):

    _id: int = 0
    _IdDict: {} 
    _titleDict: {}

class Poem(Media_Work):

  def __init__(self, id, title, author, content, age, mtype, verbs):

    super().__init__()
    self.id = id
    self.title = title
    self.author = author
    self.content = content
    self.age = age
    self.mtype = mtype
    self.verbs = verbs

    Poem._IdDict.update({id: self})

My error message:

AttributeError: 'Poem' object has no attribute '_IdDict'

Similar error if I change the bottom line to:

self._IdDict.update({id:self})

New error message:

AttributeError: type object 'Poem' has no attribute '_IdDict'

Answer 1

As-written, your intended dict _IdDict is really a type hint (see comment by ShadowRanger)!

Set the attribute as either a class variable (probably your intention) or assign the attribute in __init__()

---

Class Variable
Reference will be created in class declaration and shared by all instances of the class
There is no need to call super() to init in this case

class Media_Work():

    _id     = 0
    _IdDict = {}

Attribute
Reference will be created at class init and unique to each instance of the class

class Media_Work():

    def __init__(self):
        self._id     = 0
        self._IdDict = {} 

Answer 2

It is inheriting, but you haven't defined the _IdDict class attribute. _IdDict: {} is type hint, not a definition, and it's a local name in __init__, not a class attribute.

Here's an example of how to fix it. You might need to tailor this to fit your needs:

class Media_Work:
    _IdDict = {}

class Poem(Media_Work):
    def __init__(self, _id):
        Poem._IdDict.update({_id: self})

Example usage:

>>> p = Poem(17)
>>> Poem._IdDict
{17: <__main__.Poem object at 0x7f13689a3ba8>}
>>> Media_Work._IdDict
{17: <__main__.Poem object at 0x7f13689a3ba8>}

By the way, don't use id as a variable name, since it's a builtin.

Answer 3

[My previous version of this answer was lacking].... You have two issues there. The first is that you failed to assign a value to _IdDict so it was not created. Second, you defined it in the wrong scope. If you wanted to create a Class attribute you need to refer to it as Media_Work._IdDict from within the __init__ method or you needed to define it outside the method. Such as:

class Media_Work(object):

    _id: int = 0
    _IdDict: {} = {}
    _titleDict: {} = {}

    def __init__(self):
        Media_Work._id = 0