[docs] [issue21949] Document the Py_SIZE() macro.

Gregory P. Smith report at bugs.python.org
Wed Jul 9 21:44:44 CEST 2014

New submission from Gregory P. Smith:

The Py_SIZE() macro is not documented.  It should be.  It is very useful along with PyList_New(positive_number) after using PyList_SET_ITEM() to fill in up to the first positive_number elements of a list object in the most optimal manner by avoiding numerous redundant array resizes and error checks along the away.

The Py_SIZE() macro was introduced (in 2.6 I believe) and is specifically intended for use as an lvalue (see http://bugs.python.org/issue1724 to confirm that).  It currently has uses in several places in CPython's core and modules as well as within some third party extension modules and tools such as Cython).

assignee: docs at python
components: Documentation
keywords: easy
messages: 222633
nosy: docs at python, gregory.p.smith
priority: normal
severity: normal
status: open
title: Document the Py_SIZE() macro.
type: performance
versions: Python 2.7, Python 3.4, Python 3.5

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