[ python-Bugs-1207379 ] class property fset not working

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Bugs item #1207379, was opened at 2005-05-23 17:02
Message generated for change (Settings changed) made by rhettinger
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Category: Documentation
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Master_Jaf (master_jaf)
>Assigned to: Raymond Hettinger (rhettinger)
Summary: class property fset not working

Initial Comment:
Classes which are not instantiated from 'object',
containing properties, are not working as expected. The
GET method is working but not the SET method. Tested
with python 2.4.1 und 2.3.5.
See sample code file.

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Comment By: Reinhold Birkenfeld (birkenfeld)
Date: 2005-06-04 05:27

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Attaching a patch for the Tutorial. It adds the following
sentence:

+Note that with Python 2.2, a new kind of classes was
introduced:
+A class deriving from \class{object} is called a
\emph{new-style class}.
+The differences to classic classes are mostly internal, but
there are
+some features (like properties and static methods) that are
only
+available for new-style classes.
+


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Comment By: Master_Jaf (master_jaf)
Date: 2005-05-26 13:59

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>From my point of view (I'm just learning Python) there is only a
simple difference between old and new style classes, just the
(object) while defining a class.
For sure, we can close this. My questions were answered :-)

So my suggestions for adding info to the documentation:

"Python Tutorial": Chap. 9.3., ex.
With Python 2.2 new style classes were introduced. These new 
style classes are inherited from 'object' base class and
supporting
newer features like properties, slots etc.. It is
recommended to use
new style classes.

"Python Library Reference": Chap. 2.1 Built-in Functions, ex.
property([fget[, fset[, fdel[, doc]]]])
  [....]
New in Python 2.2. Properties only can applied to new style
classes. See also "D. Glossary" -> new style classes for more
details.

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Comment By: Terry J. Reedy (tjreedy)
Date: 2005-05-26 11:37

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For people who learned Python with old-style classes, it 
is 'obvious' that properties are a new addition that came with and 
work with new-style classes.  Can you suggest specific places in 
the docs where clarification could be made?  Or should be close 
this?

(I suspect that setting is more complicated than getting but would 
not have expected even the get method to work.)

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Comment By: Master_Jaf (master_jaf)
Date: 2005-05-24 07:27

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After reading some more documentation I've found at Python
Tutorial "D. Glossary" more hints.
<cite>
Any class that inherits from object. This includes all
built-in types like list and dict. Only new-style classes
can use Python's newer, versatile features like __slots__,
descriptors, properties, __getattribute__(), class methods,
and static methods.
</cite>
Fine. OK, understood..
I'm tending to agree with mwh's opinion, that this is a
documentation bug, although I don't fully understand why the
GET descriptor is working but unlikly not the SET descriptor.

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Comment By: Michael Hudson (mwh)
Date: 2005-05-24 02:58

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At the very limit, this is a documentation bug.  Why did you think 
properties could be attached to old-style classes?

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