[Zope] Re: Error:unbound method init() must be called with instance as first argument

12 Apr 2004

      On Fri, 9 Apr 2004 16:28:38 +0400
"Serg" <sutni@yandex.ru> wrote:
...
--- file A.py ---
class CA:
    "class for my needs"
    def __init__(self, a=0):
        "init"
        self.__a=a
--- file B.py ---
from A import CA
from OFS import SimpleItem
class CB(SimpleItem.SimpleItem , CA ):
    "class B"
    def __init__(self, id, docN):
        "init"
        CA.__init__(self)
        self.id=id
        self.docN=docN
On add object of CB Zope write:
        Site Error
        An error was encountered while publishing this resource.
        Error Type: TypeError
        Error Value: unbound method __init__() must be called with
        instance
as first argument
Where is this Error?
The error is that CB and CA are different types. CA is a classic python
class. CB is an ExtensionClass (because it subclasses SimpleItem which
subclasses ExtensionClass.Base). Python is preventing you from binding
the non-extension class CA to the CB extension class intance.

A solution is to make CA an extension class::

  import ExtensionClass

  class CA(ExtensionClass.Base):
      ...

Then delegating to CA's __init__ from CB should work fine. This is the
reason why you will often see mix-in classes in Zope inherit from
ExtensionClass.Base even though they do not explicitly use its features.

-Casey

[Zope] Re: Error:unbound method __init__() must be called with instance as first argument

Casey Duncan

[Zope] Re: Error:unbound method init() must be called with instance as first argument