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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
Lib/opcode.py
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@ -139,7 +139,7 @@ hasconst.append(100)
name_op('LOAD_NAME', 101) # Index in name list
def_op('BUILD_TUPLE', 102) # Number of tuple items
def_op('BUILD_LIST', 103) # Number of list items
def_op('BUILD_MAP', 104) # Always zero for now
def_op('BUILD_MAP', 104) # Number of dict entries (upto 255)
name_op('LOAD_ATTR', 105) # Index in name list
def_op('COMPARE_OP', 106) # Comparison operator
hascompare.append(106)