[issue36401] Readonly properties should be marked as such in help()

[Stéphane Wirtel]

Stéphane Wirtel  added the comment:

Hi Raymond,

About the C API, I wanted to know that because I started to use neovim
for the development of CPython mix between C and Python is really great
with this tool. Also, I wanted to have the description of the C parts,
example, when I have PyArg_ParseTupleAndKeywords under the cursor, with
(n)vim I could use the K shortcut and see the description of this
function via the keywordprg of vim.

But we have the result from Sphinx, because the C part is described in
the .rst files. So, maybe I could develop a wrapper for Sphinx and the
manpages.

So, thank you for your PR.

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[issue36401] Readonly properties should be marked as such in help()

[Raymond Hettinger]

Change by Raymond Hettinger :


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resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

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[issue36401] Readonly properties should be marked as such in help()

[Raymond Hettinger]

Raymond Hettinger  added the comment:


New changeset 62be33870e2f8517314bf9c7275548e799296f7e by Raymond Hettinger in 
branch 'master':
bpo-36401: Have help() show readonly properties separately (GH-12517)
https://github.com/python/cpython/commit/62be33870e2f8517314bf9c7275548e799296f7e


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[issue36401] Readonly properties should be marked as such in help()

[Raymond Hettinger]

Change by Raymond Hettinger :


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keywords: +patch
pull_requests: +12468
stage:  -> patch review

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[issue36401] Readonly properties should be marked as such in help()

[Raymond Hettinger]

Raymond Hettinger  added the comment:

> but can we do the same thing with the PyGetSetDef declaration 
> for the C Part?

The would likely take an API change.  For now, using only what is already 
exposed in Python, we can only partition data descriptors in two groups:

* Known to be readonly because __set__ is missing or fset is None
* Possibly writeable, can't really tell until __set__ is called

Example in the latter category,  

>>> t = time.localtime()
>>> hasattr(type(t).tm_sec, '__set__')
True
>>> t.tm_sec = 31
Traceback (most recent call last):
  File "", line 1, in 
 t.tm_sec = 31
AttributeError: readonly attribute

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[issue36401] Readonly properties should be marked as such in help()

[Stéphane Wirtel]

Stéphane Wirtel  added the comment:

@Raymond

+1 

but can we do the same thing with the PyGetSetDef declaration for the C Part?

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nosy: +matrixise

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[issue36401] Readonly properties should be marked as such in help()

[Raymond Hettinger]

Raymond Hettinger  added the comment:

For property objects, we have to look at *fset* and *fdel* to find-out whether 
they are assignable:

>>> A.rop.fset is None
True
>>> A.wandr.fset is None
False

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[issue36401] Readonly properties should be marked as such in help()

[Raymond Hettinger]

New submission from Raymond Hettinger :

It is common to create read-only properties with the '@property' decoration but 
the existing help() output doesn't annotate them as such.

One way to go is to annotate each one separately:

 |  --
 |  Data descriptors inherited from _IPAddressBase:
 |  
 |  compressed (read-only property) <== NEW ANNOTATION
 |  Return the shorthand version of the IP address as a string.
 |  
 |  exploded (read-only property)   <== NEW ANNOTATION
 |  Return the longhand version of the IP address as a string.
 |  
 |  reverse_pointer (read-only property)<== NEW ANNOTATION
 |  The name of the reverse DNS pointer for the IP address, e.g.:
 |  >>> ipaddress.ip_address("127.0.0.1").reverse_pointer
 |  '1.0.0.127.in-addr.arpa'
 |  >>> ipaddress.ip_address("2001:db8::1").reverse_pointer
 |  
'1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa'


Another way to go is to break the data descriptor section into two sections --- 
isolate those that define __set__ or __delete__ from those that don't.

For example, given this code:

class A:
'Variety of descriptors and method'

__slots__ = '_w', '_x'

def __init__(self, w: int, x: str):
'initializer'
self.w = w
self.x = x

@classmethod
def cm(cls, u):
'do something with u'
return cls(u * 4)

@staticmethod
def sm(v):
'do something with v'
return v * 3

@property
def rop(self):
'computed field'
return self._w * 2

@property
def wandr(self):
'managed attribute'
return self._w

@wandr.setter
def wandr(self, w):
self._w = w


Produce this help output:

Help on class A in module __main__:

class A(builtins.object)
 |  A(w: int, x: str)
 |  
 |  Variety of descriptors and method
 |  
 |  Methods defined here:
 |  
 |  __init__(self, w: int, x: str)
 |  initializer
 |  
 |  --
 |  Class methods defined here:
 |  
 |  cm(u) from builtins.type
 |  do something with u
 |  
 |  --
 |  Static methods defined here:
 |  
 |  sm(v)
 |  do something with v
 |  
 |  --
 |  Read-only descriptors defined here:<== NEW HEADING
 |  
 |  rop
 |  computed field
 |  
 |  --
 |  Mutable data descriptors defined here: <== NEW HEADING AND SECTION  
  
 |  
 |  wandr
 |  managed attribute

--
components: Library (Lib)
messages: 338621
nosy: rhettinger
priority: normal
severity: normal
status: open
title: Readonly properties should be marked as such in help()
type: enhancement
versions: Python 3.8

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