# bit count or bit set && Python3

Discussion in 'Python' started by Charles Hixson, Oct 25, 2012.

1. ### Charles HixsonGuest

In Python3 is there any good way to count the number of on bits in an
integer (after an & operation)?
Alternatively, is there any VERY light-weight implementation of a bit
set? I'd prefer to use integers, as I'm probably going to need
thousands of these, if the tests work out. But before I can test, I
need a decent bit counter. (shift, xor, &, and | are already present
for integer values, but I also need to count the number of "true" items
after the logical operation. So if a bitset is the correct approach,
I'll need it to implement those operations, or their equivalents in
terms of union and intersection.)

Or do I need to drop into C for this?

--
Charles Hixson

Charles Hixson, Oct 25, 2012

2. ### rusiGuest

On Oct 25, 7:56 pm, Charles Hixson <> wrote:
> In Python3 is there any good way to count the number of on bits in an
> integer (after an & operation)?
> Alternatively, is there any VERY light-weight implementation of a bit
> set?  I'd prefer to use integers, as I'm probably going to need
> thousands of these, if the tests work out.  But before I can test, I
> need a decent bit counter.  (shift, xor, &, and | are already present
> for integer values, but I also need to count the number of "true" items
> after the logical operation.  So if a bitset is the correct approach,
> I'll need it to implement those operations, or their equivalents in
> terms of union and intersection.)
>
> Or do I need to drop into C for this?
>
> --
> Charles Hixson

You may have already checked it out and find it unsuitable...
I guess you know that python has good implementation of sets
http://docs.python.org/library/sets.html ?

rusi, Oct 25, 2012

3. ### Terry ReedyGuest

On 10/25/2012 12:13 PM, rusi wrote:
> On Oct 25, 7:56 pm, Charles Hixson <> wrote:
>> In Python3 is there any good way to count the number of on bits in an
>> integer (after an & operation)?
>> Alternatively, is there any VERY light-weight implementation of a bit
>> set? I'd prefer to use integers, as I'm probably going to need
>> thousands of these, if the tests work out. But before I can test, I
>> need a decent bit counter. (shift, xor, &, and | are already present
>> for integer values, but I also need to count the number of "true" items
>> after the logical operation. So if a bitset is the correct approach,
>> I'll need it to implement those operations, or their equivalents in
>> terms of union and intersection.)
>>
>> Or do I need to drop into C for this?

If I wanted 1000s of fast limited-length bitsets, I would consider using
Cython to make an extension class.

--
Terry Jan Reedy

Terry Reedy, Oct 25, 2012
4. ### Guest

On Thursday, October 25, 2012 7:56:25 AM UTC-7, Charles Hixson wrote:
> In Python3 is there any good way to count the number of on bits in an
> integer (after an & operation)?

You may want to look at gmpy2[1] and the popcount() function.

>
> Alternatively, is there any VERY light-weight implementation of a bit
> set? I'd prefer to use integers, as I'm probably going to need
> thousands of these, if the tests work out. But before I can test, I
> need a decent bit counter. (shift, xor, &, and | are already present
> for integer values, but I also need to count the number of "true" items
> after the logical operation. So if a bitset is the correct approach,
>

Whether or not gmpy2 is considered light-weight is debateable.

> I'll need it to implement those operations, or their equivalents in
> terms of union and intersection.)
>
>
>
> Or do I need to drop into C for this?
>

>
>
> --
>
> Charles Hixson

, Oct 26, 2012
5. ### Guest

On Thursday, October 25, 2012 7:56:25 AM UTC-7, Charles Hixson wrote:
> In Python3 is there any good way to count the number of on bits in an
> integer (after an & operation)?

You may want to look at gmpy2[1] and the popcount() function.

>
> Alternatively, is there any VERY light-weight implementation of a bit
> set? I'd prefer to use integers, as I'm probably going to need
> thousands of these, if the tests work out. But before I can test, I
> need a decent bit counter. (shift, xor, &, and | are already present
> for integer values, but I also need to count the number of "true" items
> after the logical operation. So if a bitset is the correct approach,
>

Whether or not gmpy2 is considered light-weight is debateable.

> I'll need it to implement those operations, or their equivalents in
> terms of union and intersection.)
>
>
>
> Or do I need to drop into C for this?
>

>
>
> --
>
> Charles Hixson

, Oct 26, 2012
6. ### Charles HixsonGuest

wrote:
> On Thursday, October 25, 2012 7:56:25 AM UTC-7, Charles Hixson wrote:
>> In Python3 is there any good way to count the number of on bits in an
>> integer (after an& operation)?

> You may want to look at gmpy2[1] and the popcount() function.
>
>> Alternatively, is there any VERY light-weight implementation of a bit
>> set? I'd prefer to use integers, as I'm probably going to need
>> thousands of these, if the tests work out. But before I can test, I
>> need a decent bit counter. (shift, xor,&, and | are already present
>> for integer values, but I also need to count the number of "true" items
>> after the logical operation. So if a bitset is the correct approach,
>>

> Whether or not gmpy2 is considered light-weight is debateable.
>
>> I'll need it to implement those operations, or their equivalents in
>> terms of union and intersection.)
>>
>>
>>
>> Or do I need to drop into C for this?
>>

>
>>
>> --
>>
>> Charles Hixson

I can see many times when that would be useful, but for this particular
case I think that bin(val).count("1") is probably the better solution.
The other options that I need are already available directly in integer
numbers, and I will be surprised if I need more than a 32-bit set, so
integers should be a reasonable approach. It doesn't seem to have the
overhead that I feared a string conversion would have (possibly because
converting an integer to a bit string is trivial), so I don't think
that gmpy would add value to this program.

Next I need to decide about weak pointers, and then shelve vs.
tokyocabinet. (I sort of don't like shelve, because of its use of
pickle, with the attendent security risks. OTOH, the file will be local
to the computer, not going over the net, which minimizes that. Still, I
may decide to reimplement it using ast.literal_eval, as I'm not
intending to store anything that it won't handle.

Charles Hixson, Oct 26, 2012