Is there no way to optimize the byte code without adding to the language?
Not that it’s a bad idea anyway, but I wonder if frozen sets are common
enough to warrant a change.
Are there any performance advantages to a frozen set? I ask because I do
often use sets that could be frozen, but don’t need to be. E.g. they don’t
change, nor are they used as keys.
For example:
If flag in {‘the’, ‘allowable’, ‘flags’}:
…
If a frozen set was even a little bit faster or used less memory, it would
be nice to be able to create one directly.
-CHB
On Sun, Jan 16, 2022 at 8:50 AM MRAB <pyt...@mrabarnett.plus.com> wrote:
> On 2022-01-16 08:27, Steven D'Aprano wrote:
> [snip]
> >>>> dis.dis("frozenset({1, 2, 3})")
> > 1 0 LOAD_NAME 0 (frozenset)
> > 2 BUILD_SET 0
> > 4 LOAD_CONST 0 (frozenset({1, 2, 3}))
> > 6 SET_UPDATE 1
> > 8 CALL_FUNCTION 1
> > 10 RETURN_VALUE
> >
> > Got that? To create a frozenset of literals, first the compiler creates
> > a frozenset constant containing what you wanted. Then at runtime, it:
> >
> > - looks up frozenset in globals and builtins;
> > - loads the pre-prepared frozenset (which is exactly what we want);
> > - creates a new set from that frozenset;
> > - calls the frozenset() function on that set to create a new frozenset
> > that duplicates the pre-prepared one;
> > - and finally garbage-collects the temporary set.
> >
> [snip]
>
> Not quite as bad as that:
>
> >>> f = frozenset({1, 2, 3})
> >>> f is frozenset(f)
> True
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--
Christopher Barker, PhD (Chris)
Python Language Consulting
- Teaching
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