[issue27725] Use Py_SIZE(x) instead of x->ob_size

[SilentGhost]

Changes by SilentGhost <ghost.adh at runbox.com>:


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components: +Interpreter Core
nosy: +facundobatista, mark.dickinson, rhettinger, skrah

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue27725>
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