#36962: Missing call to superclass `__init__` during object initialization
------------------------------+--------------------------------------
Reporter: kochrac | Owner: (none)
Type: Bug | Status: closed
Component: Core (Other) | Version: 6.0
Severity: Normal | Resolution: fixed
Keywords: | Triage Stage: Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
------------------------------+--------------------------------------
Changes (by kochrac):
* resolution: => fixed
* status: new => closed
Old description:
> [https://github.com/django/django/blob/main/django/contrib/admin/widgets.py#L94-L626
> / L94-L626]
> [https://github.com/django/django/blob/main/django/forms/widgets.py#L1116-L1116
> / L1116-L1116]
> [https://github.com/django/django/blob/main/django/contrib/gis/forms/widgets.py#L12-L12
> / L12-L12]
> [https://github.com/django/django/blob/main/django/db/models/expressions.py#L1880-L1880
> / L1880-L1880]
> [https://github.com/django/django/blob/main/django/core/handlers/wsgi.py#L56-L56
> / L56-L56]
> [https://github.com/django/django/blob/main/django/template/defaulttags.py#L909-L909
> / L909-L909]
> [https://github.com/django/django/blob/main/django/contrib/admin/widgets.py#L630-L630
> / L630-L630]
> [https://github.com/django/django/blob/main/django/contrib/gis/db/backends/oracle/adapter.py#L7-L7
> / L7-L7]
> [https://github.com/django/django/blob/main/django/db/backends/ddl_references.py#L72-L72
> / L72-L72]
> [https://github.com/django/django/blob/main/django/contrib/admin/widgets.py#L262-L262
> / L262-L262]
>
>
> **Missing call to superclass __init__ during object initialization**
> Pythonunlike some other object-oriented languages such as Java, allows
> the developer complete freedom in when and how superclass initializers
> are called during object initialization. However, the developer has
> responsibility for ensuring that objects are properly initialized, and
> that all superclass `__init__` methods are called.
>
> If the `__init__` method of a superclass is not called during object
> initialization, this can lead to errors due to the object not being fully
> initialized, such as having missing attributes. A call to the `__init__`
> method of a superclass during object initialization may be
> unintentionally skipped:
>
> - If a subclass calls the `__init__` method of the wrong class.
> - If a call to the `__init__` method of one its base classes is omitted.
> - If a call to `super().__init__` is used, but not all `__init__` methods
> in the Method Resolution Order (MRO) chain themselves call `super()`.
> This in particular arises more often in cases of multiple inheritance.
>
> explicit calls to __init__ are used, but SportsCar erroneously calls
> Vehicle.__init__. This is fixed in FixedSportsCar by calling
> Car.__init__.
>
> {{{
> class Vehicle(object):
>
> def __init__(self):
> self.mobile = True
>
> class Car(Vehicle):
>
> def __init__(self):
> Vehicle.__init__(self)
> self.car_init()
>
> class SportsCar(Car, Vehicle):
>
> def __init__(self):
> Vehicle.__init__(self)
> self.sports_car_init()
>
> class FixedSportsCar(Car, Vehicle):
>
> def __init__(self):
> Car.__init__(self)
> self.sports_car_init()
> }}}
> **References**
> [https://docs.python.org/3/reference/datamodel.html#object.__init__ /
> Python init]
> [https://docs.python.org/3/reference/datamodel.html#object.__init__ /
> Python Standard Library super]
> [https://docs.python.org/3/glossary.html#term-method-resolution-order /
> Python Glossary Method resolution order]
New description:
[https://github.com/django/django/blob/main/django/contrib/admin/widgets.py#L94-L626
/ L94-L626]
[https://github.com/django/django/blob/main/django/forms/widgets.py#L1116-L1116
/ L1116-L1116]
[https://github.com/django/django/blob/main/django/contrib/gis/forms/widgets.py#L12-L12
/ L12-L12]
[https://github.com/django/django/blob/main/django/db/models/expressions.py#L1880-L1880
/ L1880-L1880]
[https://github.com/django/django/blob/main/django/core/handlers/wsgi.py#L56-L56
/ L56-L56]
[https://github.com/django/django/blob/main/django/template/defaulttags.py#L909-L909
/ L909-L909]
[https://github.com/django/django/blob/main/django/contrib/admin/widgets.py#L630-L630
/ L630-L630]
[https://github.com/django/django/blob/main/django/contrib/gis/db/backends/oracle/adapter.py#L7-L7
/ L7-L7]
[https://github.com/django/django/blob/main/django/db/backends/ddl_references.py#L72-L72
/ L72-L72]
[https://github.com/django/django/blob/main/django/contrib/admin/widgets.py#L262-L262
/ L262-L262]
**Missing call to superclass __init__ during object initialization**
Pythonunlike some other object-oriented languages such as Java, allows the
developer complete freedom in when and how superclass initializers are
called during object initialization. However, the developer has
responsibility for ensuring that objects are properly initialized, and
that all superclass `__init__` methods are called.
If the `__init__` method of a superclass is not called during object
initialization, this can lead to errors due to the object not being fully
initialized, such as having missing attributes. A call to the `__init__`
method of a superclass during object initialization may be unintentionally
skipped:
- If a subclass calls the `__init__` method of the wrong class.
- If a call to the `__init__` method of one its base classes is omitted.
- If a call to `super().__init__` is used, but not all `__init__` methods
in the Method Resolution Order (MRO) chain themselves call `super()`. This
in particular arises more often in cases of multiple inheritance.
explicit calls to __init__ are used, but SportsCar erroneously calls
Vehicle.__init__. This is fixed in FixedSportsCar by calling Car.__init__.
{{{
class Vehicle(object):
def __init__(self):
self.mobile = True
class Car(Vehicle):
def __init__(self):
Vehicle.__init__(self)
self.car_init()
class SportsCar(Car, Vehicle):
def __init__(self):
Vehicle.__init__(self)
self.sports_car_init()
class FixedSportsCar(Car, Vehicle):
def __init__(self):
Car.__init__(self)
self.sports_car_init()
}}}
**References**
[https://docs.python.org/3/reference/datamodel.html#object.__init__ /
Python init]
[https://docs.python.org/3/reference/datamodel.html#object.__init__ /
Python Standard Library super]
[https://docs.python.org/3/glossary.html#term-method-resolution-order /
Python Glossary Method resolution order]
--
Comment:
Requested fix as https://github.com/django/django/pull/20804
--
Ticket URL: <https://code.djangoproject.com/ticket/36962#comment:1>
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