On 26/06/2018 12:39, Chris Angelico wrote:
On Tue, Jun 26, 2018 at 9:30 PM, Bart <b...@freeuk.com> wrote:
On 19/06/2018 11:33, Steven D'Aprano wrote:
On Tue, 19 Jun 2018 10:19:15 +0100, Bart wrote:
* Integer sets (Pascal-like sets)
Why do you need them if you have real sets?
I tried Python sets for the first time. They seemed workable but rather
clunky to set up. But here is one problem on my CPython:
x = set(range(10_000_000))
This used up 460MB of RAM (the original 100M I tried exhausted the memory).
The advantage of Pascal-style sets is that that same set will occupy only
1.25MB, as it is a bit-map.
While sets will not usually be that big, there might be lots of small sets
and they all add up.
Cool. Make me a bitset that can represent this Python set:
{-5, -4, 6, 10, 1.5, "spam", print}
Why? It's a set of integer values with a huge range of applications.
Here's the set of characters allowed in a C identifier (not using Python
syntax):
cident = {'A'..'Z', 'a'..'z', '0'..'9', '_', '9'}
The characters allowed in a hex constant:
{'0'..'9', 'A'..'F', 'a'..'f'}
A set representing every Unicode character, except those which can be C
identifiers:
{0..1_114_111} - cident
The latter taking only 136KB rather than 64MB as it seemed to.
I don't know whether there is a direct equivalent in Python (I thought
somebody would point it out), apart from ways to construct similar
functionality with bit-arrays (but then, every language can have such
sets if you take the DIY approach).
Steven asked why I need them when there are 'real' sets, and I answered
that.
--
bart
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