[issue1229239] optionally allow mutable builtin types

[Daniel Diniz]

Changes by Daniel Diniz <ajaksu at gmail.com>:


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stage:  -> test needed
type:  -> feature request
versions: +Python 2.7 -Python 2.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue1229239>
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