Wrong function calls and referring to not removed concepts in descriptor HowTo (documentation)

[DavidBecher]

BPO	25435
Nosy	@rhettinger, @dholth, @vadmium, @eryksun, @marco-buttu, @Mariatta
Files	21.diff.txt

^{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 = 'https://github.com/rhettinger'
closed_at = <Date 2019-08-29.06:46:53.357>
created_at = <Date 2015-10-18.18:49:49.065>
labels = ['3.7', 'docs']
title = 'Wrong function calls and referring to not removed concepts in descriptor HowTo (documentation)'
updated_at = <Date 2019-08-29.06:46:53.356>
user = 'https://bugs.python.org/DavidBecher'

bugs.python.org fields:

activity = <Date 2019-08-29.06:46:53.356>
actor = 'rhettinger'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2019-08-29.06:46:53.357>
closer = 'rhettinger'
components = ['Documentation']
creation = <Date 2015-10-18.18:49:49.065>
creator = 'David Becher'
dependencies = []
files = ['40812']
hgrepos = []
issue_num = 25435
keywords = []
message_count = 12.0
messages = ['253159', '253165', '253168', '253202', '270007', '270014', '293162', '293163', '293237', '293252', '302921', '350735']
nosy_count = 8.0
nosy_names = ['rhettinger', 'dholth', 'docs@python', 'martin.panter', 'eryksun', 'marco.buttu', 'David Becher', 'Mariatta']
pr_nums = []
priority = 'normal'
resolution = 'out of date'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue25435'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7']

[DavidBecher]

Since Python 3 removed unbound methods, I found some references using the old terminology in this HowTo about descriptors (https://docs.python.org/3/howto/descriptor.html). Also, since unbound methods have been removed, the function call types.MethodType now only takes two arguments, namely the function to bind and the object to bind to. In the current documentation, however, the old function call with three arguments is still being used.

I made a pull request on github, then I realized that it is just a mirror repo. Attached you will see a patch file with some of the obvious changes that could me made to the document

[vadmium]

Thanks for the patch. I left a few comments on the code review. I think the class is meant to represent a real function object, not a wrapper. And it would be good to update the following paragraphs about unbound methods.

Also, it looks like the rest of that page could do with some other updates. E.g. no need for explicit Function(object) base class, no need to mention that a method exists in Python 2.3, code could use @classmethod decorator syntax. But these are a slightly separate issues.

[vadmium]

Also further up the page, “unbound methods . . . are . . . based on the descriptor protocol” is probably not really correct or useful. bpo-23702 is already open about mentioning unbound methods.

[rhettinger]

I'll update this document to reflect the current state of the world.

[dholth]

This bit me also. Is there other documentation for how many arguments MethodType() should take?

[eryksun]

I'm surprised it's not documented for the types module:

https://docs.python.org/3.5/library/types.html#types.MethodType

At least the docstring has the parameters:

    >>> print(types.MethodType.__doc__)
    method(function, instance)
    
    Create a bound instance method object.

[vadmium]

Raymond I suggest you unassign this and let others work on it.

[rhettinger]

I will have a chance to work on this before long.

[marco-buttu]

I also noticed that the howto differentiates between objects and classes:

"The details of invocation depend on whether obj is an object or a class."

I think it is misleading, because a class is actually an object. IMHO is better to differentiate between classes and non-classes objects:

"The details of invocation depend on whether obj is a class or not."

[rhettinger]

I think it is misleading, because a class is actually an object.

This is only misleading *after* you know all the interesting details about Python and metaclasses. Prior to that, it is a reasonable and important distinction that I don't want to get lost in weasel words. The calls from object.__getattribute__ are different that those from type.__getattribute__. Likewise, data and non-data descriptors can only be described in terms of objects versus classes. Lastly, descriptors only work when stored in a class, if you store them in instances, they don't get invoked.