Mercurial > cpython-lru_cache-weakref
diff Python/compile.c @ 44339:7ac117b3be37 legacy-trunk
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.
| author | Raymond Hettinger <python@rcn.com> |
|---|---|
| date | Tue, 18 Dec 2007 21:24:09 +0000 |
| parents | 07aa19170a67 |
| children | 616fec0eb514 |
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--- a/Python/compile.c Tue Dec 18 20:10:42 2007 +0000 +++ b/Python/compile.c Tue Dec 18 21:24:09 2007 +0000 @@ -2922,11 +2922,9 @@ case IfExp_kind: return compiler_ifexp(c, e); case Dict_kind: - /* XXX get rid of arg? */ - ADDOP_I(c, BUILD_MAP, 0); n = asdl_seq_LEN(e->v.Dict.values); - /* We must arrange things just right for STORE_SUBSCR. - It wants the stack to look like (value) (dict) (key) */ + ADDOP_I(c, BUILD_MAP, (n>255 ? 255 : n)); + n = asdl_seq_LEN(e->v.Dict.values); for (i = 0; i < n; i++) { VISIT(c, expr, (expr_ty)asdl_seq_GET(e->v.Dict.values, i));