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Don't mention __slots__ as a technique for error avoidance

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Andrew M. Kuchling 2003-05-20 18:12:21 +00:00
parent e960e22579
commit 28137a09d6
1 changed files with 6 additions and 10 deletions
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16
Doc/whatsnew/whatsnew22.tex
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@ -424,14 +424,9 @@ Finally, it's possible to constrain the list of attributes that can be
referenced on an object using the new \member{__slots__} class attribute. referenced on an object using the new \member{__slots__} class attribute.
Python objects are usually very dynamic; at any time it's possible to Python objects are usually very dynamic; at any time it's possible to
define a new attribute on an instance by just doing define a new attribute on an instance by just doing
\code{obj.new_attr=1}. This is flexible and convenient, but this \code{obj.new_attr=1}. A new-style class can define a class attribute named
flexibility can also lead to bugs, as when you meant to write \member{__slots__} to limit the legal attributes
\code{obj.template = 'a'} but made a typo and wrote to a particular set of names. An example will make this clear:
\code{obj.templtae} by accident.
A new-style class can define a class attribute named \member{__slots__}
to constrain the list of legal attribute names. An example will make
this clear:
\begin{verbatim} \begin{verbatim}
>>> class C(object): >>> class C(object):
@ -443,16 +438,17 @@ None
>>> obj.template = 'Test' >>> obj.template = 'Test'
>>> print obj.template >>> print obj.template
Test Test
>>> obj.templtae = None >>> obj.newattr = None
Traceback (most recent call last): Traceback (most recent call last):
File "<stdin>", line 1, in ? File "<stdin>", line 1, in ?
AttributeError: 'C' object has no attribute 'templtae' AttributeError: 'C' object has no attribute 'newattr'
\end{verbatim} \end{verbatim}
Note how you get an \exception{AttributeError} on the attempt to Note how you get an \exception{AttributeError} on the attempt to
assign to an attribute not listed in \member{__slots__}. assign to an attribute not listed in \member{__slots__}.
\subsection{Related Links} \subsection{Related Links}
\label{sect-rellinks} \label{sect-rellinks}