[issue38099] __dict__ attribute is incorrectly stated to be read-only

[Reed]

Reed  added the comment:

Thank you for the clarification. I didn't realize the section only referred to 
types, but it makes sense now that I read the documentation more carefully.

The documentation is still incorrect for certain attributes (e.g. __bases__ and 
__name__) as they can be mutated. For example:

class A: pass
A.__name__ = 'AA'

class B(A): pass
class C(B): pass
C.__bases__ = (A,)

Also, this documentation is incorrectly linked to by other parts of the 
documentation. For example, in 
https://docs.python.org/3/reference/datamodel.html#the-standard-type-hierarchy, 
there is the sentence:

"Special attributes: __dict__ is the attribute dictionary; __class__ is the 
instance’s class."

__dict__ and __class__ link to the documentation about types, and yet that 
sentence is referring to all instances of any class (such as `A()`), not just 
type objects (such as `A`).

In terms of concrete improves, I would suggest:
* Adding a section somewhere describing __dict__ and __class__ for all 
instances, not just types. Or change the original section to refer to all 
instances.

Assuming the original section is not changed to refer to all instances:
* In the sentence "The implementation adds a few special read-only 
attributes to several object types", replace "object types" with "types" or 
"instances whose class subclasses from `type`" 
* Replace `instance.class` with `class.class`. The phrase `instance` is 
confusing, as it then describes `class.__bases__`, which does explicitly use 
the word "class" to indicate it only applies to classes.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue38099] __dict__ attribute is incorrectly stated to be read-only

[Steven D'Aprano]

Steven D'Aprano  added the comment:

Oh, another point... 

Python is a little more complicated than some other languages, like Java, 
because Python classes (types) are themselves instances (objects) of yet 
another class (the so called "metaclass"). Ultimately, all classes are 
instances of the special metaclass called "type".

So all instances are objects, and all classes are also objects.

This is really powerful and useful, but it does sometimes make it hard to talk 
about things :-)

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue38099] __dict__ attribute is incorrectly stated to be read-only

[Steven D'Aprano]

Steven D'Aprano  added the comment:

"The implementation adds a few special read-only attributes to several object 
TYPES" [emphasis added]

py> class MyType:
... pass
...
py> MyType.__dict__ = {}
Traceback (most recent call last):
  File "", line 1, in 
AttributeError: attribute '__dict__' of 'type' objects is not writable



> What is the difference between an object and an instance?

In general, nothing. But ``object.__dict__`` refers to the special builtin 
*class* called "object". In hindsight, we should have called it Object, so we 
could more easily distinguish between the *class* called "object" and 
*instances* of that class.


py> print(object)  # the class/type itself


py> print(object())  # an instance of object


The docs are correct here, but if you care to suggest some improvements, we 
will consider them.

--
nosy: +steven.daprano

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue38099] __dict__ attribute is incorrectly stated to be read-only

[Reed]

New submission from Reed :

The documentation in this section 
(https://docs.python.org/3/library/stdtypes.html#special-attributes) states 
that the __dict__ attribute, and several others, are read-only. In particular, 
it states:

"The implementation adds a few special read-only attributes to several object 
types, where they are relevant."

Then it lists several attributes, including __dict__. However, __dict__ is 
writable. For example:

class A: pass 
A().__dict__ = {'x': 1}

Most other listed attributes, such as __class__ and __name__, are writable as 
well. They should not be documented as read-only.

(Also, I'm not sure why the documentation lists object.__dict__ and 
instance.__class__. What is the difference between an object and an instance?)

--
assignee: docs@python
components: Documentation
messages: 351765
nosy: docs@python, reed
priority: normal
severity: normal
status: open
title: __dict__ attribute is incorrectly stated to be read-only
type: enhancement
versions: Python 3.7

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com