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Merged revisions 74817-74820,74822-74824 via svnmerge from

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  r74817 | georg.brandl | 2009-09-16 11:05:11 +0200 (Mi, 16 Sep 2009) | 1 line

  Make deprecation notices as visible as warnings are right now.
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  r74818 | georg.brandl | 2009-09-16 11:23:04 +0200 (Mi, 16 Sep 2009) | 1 line

  #6880: add reference to classes section in exceptions section, which comes earlier.
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  r74819 | georg.brandl | 2009-09-16 11:24:57 +0200 (Mi, 16 Sep 2009) | 1 line

  #6876: fix base class constructor invocation in example.
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  r74820 | georg.brandl | 2009-09-16 11:30:48 +0200 (Mi, 16 Sep 2009) | 1 line

  #6891: comment out dead link to Unicode article.
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  r74822 | georg.brandl | 2009-09-16 12:12:06 +0200 (Mi, 16 Sep 2009) | 1 line

  #5621: refactor description of how class/instance attributes interact on a.x=a.x+1 or augassign.
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  r74823 | georg.brandl | 2009-09-16 15:06:22 +0200 (Mi, 16 Sep 2009) | 1 line

  Remove strange trailing commas.
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  r74824 | georg.brandl | 2009-09-16 15:11:06 +0200 (Mi, 16 Sep 2009) | 1 line

  #6892: fix optparse example involving help option.
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This commit is contained in:
Georg Brandl 2009-09-16 16:00:31 +00:00
parent e32fd1d90f
commit ee8783d0fc
7 changed files with 60 additions and 33 deletions
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31
Doc/reference/simple_stmts.rst
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@ -170,6 +170,25 @@ Assignment of an object to a single target is recursively defined as follows.
perform the assignment, it raises an exception (usually but not necessarily
:exc:`AttributeError`).
.. _attr-target-note:
Note: If the object is a class instance and the attribute reference occurs on
both sides of the assignment operator, the RHS expression, ``a.x`` can access
either an instance attribute or (if no instance attribute exists) a class
attribute. The LHS target ``a.x`` is always set as an instance attribute,
creating it if necessary. Thus, the two occurrences of ``a.x`` do not
necessarily refer to the same attribute: if the RHS expression refers to a
class attribute, the LHS creates a new instance attribute as the target of the
assignment::
class Cls:
x = 3 # class variable
inst = Cls()
inst.x = inst.x + 1 # writes inst.x as 4 leaving Cls.x as 3
This description does not necessarily apply to descriptor attributes, such as
properties created with :func:`property`.
.. index::
pair: subscription; assignment
object: mutable
@ -276,16 +295,8 @@ same way as normal assignments. Similarly, with the exception of the possible
*in-place* behavior, the binary operation performed by augmented assignment is
the same as the normal binary operations.
For targets which are attribute references, the initial value is retrieved with
a :meth:`getattr` and the result is assigned with a :meth:`setattr`. Notice
that the two methods do not necessarily refer to the same variable. When
:meth:`getattr` refers to a class variable, :meth:`setattr` still writes to an
instance variable. For example::
class A:
x = 3 # class variable
a = A()
a.x += 1 # writes a.x as 4 leaving A.x as 3
For targets which are attribute references, the same :ref:`caveat about class
and instance attributes <attr-target-note>` applies as for regular assignments.
.. _assert: