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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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2
Python/ceval.c
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@ -1997,7 +1997,7 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
break;
case BUILD_MAP:
x = PyDict_New();
x = _PyDict_NewPresized((Py_ssize_t)oparg);
PUSH(x);
if (x != NULL) continue;
break;