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improve __getattribute__ documentation #48767

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lambertdw mannequin opened this issue Dec 4, 2008 · 5 comments
Closed

improve __getattribute__ documentation #48767

lambertdw mannequin opened this issue Dec 4, 2008 · 5 comments
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@birkenfeld
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docs Documentation in the Doc dir type-feature A feature request or enhancement

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@lambertdw
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lambertdw mannequin commented Dec 4, 2008

BPO 4517
Nosy @birkenfeld

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/birkenfeld'
closed_at = <Date 2008-12-05.15:29:44.863>
created_at = <Date 2008-12-04.04:34:58.074>
labels = ['type-feature', 'docs']
title = 'improve __getattribute__ documentation'
updated_at = <Date 2008-12-05.15:29:44.837>
user = 'https://bugs.python.org/LambertDW'

bugs.python.org fields:

activity = <Date 2008-12-05.15:29:44.837>
actor = 'georg.brandl'
assignee = 'georg.brandl'
closed = True
closed_date = <Date 2008-12-05.15:29:44.863>
closer = 'georg.brandl'
components = ['Documentation']
creation = <Date 2008-12-04.04:34:58.074>
creator = 'LambertDW'
dependencies = []
files = []
hgrepos = []
issue_num = 4517
keywords = []
message_count = 5.0
messages = ['76867', '76868', '77021', '77029', '77030']
nosy_count = 2.0
nosy_names = ['georg.brandl', 'LambertDW']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue4517'
versions = ['Python 3.0']
@lambertdw
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lambertdw mannequin commented Dec 4, 2008

http://docs.python.org/dev/3.0/reference/datamodel.html#special-lookup

(After fixing the link to http://docs.python.org/3.0 at http://www.python.org/doc/ (and likewise the http://docs.python.org/whatsnew/3.0.html link.)...

The comment that __getattribute__ is "Called unconditionally to
implement attribute accesses for instances of the class" gave me hope
that some combination of "meta" "super" and "sub" might let me access
__getattribute__ for expression eval('obj + another_object') despite the
special notes. I realize now the truth is that

"__getattribute__ is NEVER accessible in pure python code when the code
uses the syntax of a unary or binary operator such as a+b, ~a, len(a)."
See most of the functions in this manual section.
Also name hash, which doesn't find much explicit use but could well be
the most used python functionality. Find a smooth way to replace my
NEVER since code can obviously access __getattribute__ from the special
function.

Thank you, and great work!

@lambertdw lambertdw mannequin assigned birkenfeld Dec 4, 2008
@lambertdw lambertdw mannequin added docs Documentation in the Doc dir type-feature A feature request or enhancement labels Dec 4, 2008
@lambertdw
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lambertdw mannequin commented Dec 4, 2008 

>>> class c:
...  def __getattribute__(self,*args):
...   print('getattribute chimes in')
... 

>>> c()+3
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'c' and 'int'

@birkenfeld
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Isn't what you refer to covered by this paragraph and the following
example: "In addition to bypassing any instance attributes in the
interest of correctness, implicit special method lookup may also bypass
the __getattribute__() method even of the object’s metaclass:"?

@lambertdw
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lambertdw mannequin commented Dec 5, 2008

Yes to msg77021. However!

I'll pin the difficulty specifically to the word "may". This cost me a
lot of time.

  1. Please change the phrasing you quoted to

"... implicit special method lookup bypasses the __getattribute__()
method even of the object’s metaclass:"

  1. Please insert into the glossary a definition of "implicit special
    method lookup" that addresses the grammar or syntax that causes it
    considering monad and dyad use.

Thank you.

@birkenfeld
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I've changed "may bypass" to "generally bypasses". It doesn't happen for
all methods, but that's an implementation detail.

I've also added a glossary entry "special method" in r67579.

@ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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