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Give meaning to the oparg for BUILD_MAP: estimated size of the dictionary.

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Allows dictionaries to be pre-sized (upto 255 elements) saving time lost
to re-sizes with their attendant mallocs and re-insertions.

Has zero effect on small dictionaries (5 elements or fewer), a slight
benefit for dicts upto 22 elements (because they had to resize once
anyway), and more benefit for dicts upto 255 elements (saving multiple
resizes during the build-up and reducing the number of collisions on
the first insertions).  Beyond 255 elements, there is no addional benefit.
This commit is contained in:
Raymond Hettinger 2007-12-18 21:24:09 +00:00
parent 3c887b2802
commit fd7ed407d7
6 changed files with 26 additions and 6 deletions
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1
Include/dictobject.h
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@ -110,6 +110,7 @@ PyAPI_FUNC(Py_ssize_t) PyDict_Size(PyObject *mp);
PyAPI_FUNC(PyObject *) PyDict_Copy(PyObject *mp);
PyAPI_FUNC(int) PyDict_Contains(PyObject *mp, PyObject *key);
PyAPI_FUNC(int) _PyDict_Contains(PyObject *mp, PyObject *key, long hash);
PyAPI_FUNC(PyObject *) _PyDict_NewPresized(Py_ssize_t minused);
/* PyDict_Update(mp, other) is equivalent to PyDict_Merge(mp, other, 1). */
PyAPI_FUNC(int) PyDict_Update(PyObject *mp, PyObject *other);