[doc] SocketType changed in Python 3

[vadmium]

BPO	27379
Nosy	@vadmium, @shihai1991
PRs	bpo-27379: In order to keep backward compatibility, update SocketType's type #14710

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-06-24.03:19:57.757>
labels = ['3.8', '3.9']
title = 'SocketType changed in Python 3'
updated_at = <Date 2020-01-17.12:28:51.267>
user = 'https://github.com/vadmium'

bugs.python.org fields:

activity = <Date 2020-01-17.12:28:51.267>
actor = 'cheryl.sabella'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2016-06-24.03:19:57.757>
creator = 'martin.panter'
dependencies = []
files = []
hgrepos = []
issue_num = 27379
keywords = ['patch']
message_count = 3.0
messages = ['269153', '347691', '349126']
nosy_count = 2.0
nosy_names = ['martin.panter', 'shihai1991']
pr_nums = ['14710']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue27379'
versions = ['Python 3.8', 'Python 3.9']

[vadmium]

In the documentation for Python 2 and 3, socket.SocketType is defined as:

This is a Python type object that represents the socket object type. It is the same as “type(socket(...))”.

In Python 2 it is a standalone “socket._socketobject” class, which holds a “_socket.socket” instance as an internal “_sock” attribute. So the documentation and implementation are consistent. But since revision 8e062e572ea4, Python 3 no longer defines SocketType directly, and just imports the “_socket.SocketType” definition, which is an alias of “_socket.socket”. The change also defines “socket.socket” as a subclass of this low-level class. The result is that SocketType is not the exact type, but only a base class:

>>> s = socket.socket()
>>> type(s)
<class 'socket.socket' at 0x2347d48>
>>> SocketType
<class '_socket.socket' at 0x7ff9e2522280>
>>> type(s) is SocketType  # Should be true according to documentation
False
>>> isinstance(s, SocketType)
True

Should the documentation just be amended, or should SocketType be changed? If SocketType is not changed, perhaps we should document that socket.socket() is a class, not just a function, and maybe deprecate SocketType.

[shihai1991]

In order to keep back compatible, I would prefer to update SocketType ;)

[shihai1991]

ping

[iritkatriel]

I don't think backwards compatibility with python 2 matters anymore. A doc fix should do.

[shihai1991]

I don't think backwards compatibility with python 2 matters anymore. A doc fix should do.

Agree. I closed #14710.

[xiaochen7]

In the previous commit, the SocketType was changed to the base class for the Socket object type. I created a PR to update the SocketType documentation. Please correct me if there is a different opinion.