Give meaning to the oparg for BUILD_MAP: estimated size of the dictionary.
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.
diff --git a/Lib/opcode.py b/Lib/opcode.py
index c3457d0..cee5057 100644
--- a/Lib/opcode.py
+++ b/Lib/opcode.py
@@ -139,7 +139,7 @@
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)