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> On 13 Nov 2023, at 15:16, Dom Grigonis via Python-list <python-list@python.org> wrote:
>
> I think it could be useful to have `xor` builtin, which has API similar to the one of `any` and `all`.

I do not understand how xor(iterator) works.
I thought xor takes exactly 2 args.

I also do not understand how xor can be short circuited.
For AND or OR only looking at the first arg works.
But that does not work for xor right?

Barry


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Well yes, I don’t think naming is very accurate. If iterable has 2 elements, then it is `xor`, otherwise it is something else - it checks the number of truth values in iterable.

Short circuiting happens, when:
xor([True, True, False, False], n=1)
At index 1 it is clear that the answer is false.

Regards,
DG

> On 13 Nov 2023, at 19:42, Barry <barry@barrys-emacs.org> wrote:
>
>
>
>> On 13 Nov 2023, at 15:16, Dom Grigonis via Python-list <python-list@python.org> wrote:
>>
>> I think it could be useful to have `xor` builtin, which has API similar to the one of `any` and `all`.
>
> I do not understand how xor(iterator) works.
> I thought xor takes exactly 2 args.
>
> I also do not understand how xor can be short circuited.
> For AND or OR only looking at the first arg works.
> But that does not work for xor right?
>
> Barry
>
>

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> On 13 Nov 2023, at 17:48, Dom Grigonis <dom.grigonis@gmail.com> wrote:
>
> Short circuiting happens, when:
> xor([True, True, False, False], n=1)
> At index 1 it is clear that the answer is false.

Can you share an example with 4 values that is true?
And explain why it is xor.

Barry

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I don't think an exclusive-or/truthy-entries-count-checker needs to be a
builtin by any stretch.

>>> def xor( iterable, n = 1 ):
... return sum( map( bool, iterable ) ) == n

Or if you insist on short circuiting:

>>> def xor_ss( iterable, n = 1 ):
... for intermediate in itertools.accumulate( iterable, (lambda x, y: x +
bool(y)), initial = 0 ):
... if intermediate > n:
... return False
... return intermediate == n



On Mon, Nov 13, 2023 at 4:05?PM Barry via Python-list <
python-list@python.org> wrote:

>
>
> > On 13 Nov 2023, at 17:48, Dom Grigonis <dom.grigonis@gmail.com> wrote:
> >
> > Short circuiting happens, when:
> > xor([True, True, False, False], n=1)
> > At index 1 it is clear that the answer is false.
>
> Can you share an example with 4 values that is true?
> And explain why it is xor.
>
> Barry
>
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> https://mail.python.org/mailman/listinfo/python-list
>
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Barry <barry@barrys-emacs.org> writes:

> I do not understand how xor(iterator) works.
> I thought xor takes exactly 2 args.

See

https://mathworld.wolfram.com/XOR.html

for some background (I was not aware of any generalizations for more
than 2 arguments either).

> I also do not understand how xor can be short circuited.

Me neither, but that could be related to the meaning of n (which I did
not get) in the OP's question. Maybe he can clarify.

Best regards

Axel
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On 2023-11-13 21:03, Barry via Python-list wrote:
>
>
>> On 13 Nov 2023, at 17:48, Dom Grigonis <dom.grigonis@gmail.com> wrote:
>>
>> Short circuiting happens, when:
>> xor([True, True, False, False], n=1)
>> At index 1 it is clear that the answer is false.
>
> Can you share an example with 4 values that is true?
> And explain why it is xor.
>
I think what the OP wants is something that stops after finding n true
items.

It's a more general form of what 'any' and 'all' do - 'any' stops when
it finds 1 true item and 'all' stops when it finds 1 false item.

In general, you might want to stop when you find n true items or n false
items, or whatever.

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xor([True, False, False, False], n=1)
xor([False, False, False, True], n=1)
Both of the above would evaluate to true.

Well, it depends how you interpret it.
In binary case it reads: “exclusively one positive bit or the other, but not both”
In this case one could read: “exclusively one positive set of certain length, but not more than one such set at the same time"

But I completely see how one could argue, that “exclusive” refers to slightly different thing. And multivariate `xor` is a function which defines fixed subsets out of which only one is true, but not the others, but this is theoretical, as in practice each set would need to always have all values switched on or off, which boils down to my proposed `xor` with `n=1`.

But the point is if there is a need for such function or I am the only one who happens to use it.

DG

> On 13 Nov 2023, at 23:03, Barry <barry@barrys-emacs.org> wrote:
>
>
>
>> On 13 Nov 2023, at 17:48, Dom Grigonis <dom.grigonis@gmail.com> wrote:
>>
>> Short circuiting happens, when:
>> xor([True, True, False, False], n=1)
>> At index 1 it is clear that the answer is false.
>
> Can you share an example with 4 values that is true?
> And explain why it is xor.
>
> Barry
>

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On Tue, 14 Nov 2023 at 08:57, Axel Reichert via Python-list
<python-list@python.org> wrote:
>
> Barry <barry@barrys-emacs.org> writes:
>
> > I do not understand how xor(iterator) works.
> > I thought xor takes exactly 2 args.
>
> See
>
> https://mathworld.wolfram.com/XOR.html
>
> for some background (I was not aware of any generalizations for more
> than 2 arguments either).
>

Generalization to more arguments usually means calculating parity -
that is, it tells you whether you have an odd or even number of true
results. Which means that short-circuiting is nonsensical.

ChrisA
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Benchmarks:
test1 = [False] * 100 + [True] * 2
test2 = [True] * 100 + [False] * 2

TIMER.repeat([.
lambda: xor(test1), # 0.0168
lambda: xor(test2), # 0.0172
lambda: xor_ss(test1), # 0.1392
lambda: xor_ss(test2), # 0.0084
lambda: xor_new(test1), # 0.0116
lambda: xor_new(test2), # 0.0074
lambda: all(test1), # 0.0016
lambda: all(test2) # 0.0046
])
Your first function is fairly slow.
Second one deals with short-circuiting, but is super slow on full search.

`xor_new` is the best what I could achieve using python builtins.

But builtin `all` has the best performance.

DG

> On 13 Nov 2023, at 23:20, Michael Speer <knomenet@gmail.com> wrote:
>
> I don't think an exclusive-or/truthy-entries-count-checker needs to be a builtin by any stretch.
>
> >>> def xor( iterable, n = 1 ):
> ... return sum( map( bool, iterable ) ) == n
>
> Or if you insist on short circuiting:
>
> >>> def xor_ss( iterable, n = 1 ):
> ... for intermediate in itertools.accumulate( iterable, (lambda x, y: x + bool(y)), initial = 0 ):
> ... if intermediate > n:
> ... return False
> ... return intermediate == n
>
>
>
> On Mon, Nov 13, 2023 at 4:05?PM Barry via Python-list <python-list@python.org <mailto:python-list@python.org>> wrote:
>
>
> > On 13 Nov 2023, at 17:48, Dom Grigonis <dom.grigonis@gmail.com <mailto:dom.grigonis@gmail.com>> wrote:
> >
> > Short circuiting happens, when:
> > xor([True, True, False, False], n=1)
> > At index 1 it is clear that the answer is false.
>
> Can you share an example with 4 values that is true?
> And explain why it is xor.
>
> Barry
>
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> https://mail.python.org/mailman/listinfo/python-list <https://mail.python.org/mailman/listinfo/python-list>

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On 2023-11-13, Dom Grigonis via Python-list <python-list@python.org> wrote:
> Hi All,
>
> I think it could be useful to have `xor` builtin, which has API similar to the one of `any` and `all`.
>
> * Also, it could have optional second argument `n=1`, which
> * indicates how many positives indicates `True` return. For
> * complete flexibility 3rd argument could indicate if `the number`
> * is equal, greater, less, ... than `n`

I would expect "xor" to return true if there are an odd number of
trues, and false if there are an even number of trues. It's not clear
to me what you're asking for.



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I am not asking. Just inquiring if the function that I described could be useful for more people.

Which is: a function with API that of `all` and `any` and returns `True` if specified number of elements is True.

It is not a generalised `xor` in strict programatic space. I.e. NOT bitwise xor applied to many bits.
This is more in line with cases that `any` and `all` builtins are used.

> On 14 Nov 2023, at 00:51, Grant Edwards via Python-list <python-list@python.org> wrote:
>
> On 2023-11-13, Dom Grigonis via Python-list <python-list@python.org> wrote:
>> Hi All,
>>
>> I think it could be useful to have `xor` builtin, which has API similar to the one of `any` and `all`.
>>
>> * Also, it could have optional second argument `n=1`, which
>> * indicates how many positives indicates `True` return. For
>> * complete flexibility 3rd argument could indicate if `the number`
>> * is equal, greater, less, ... than `n`
>
> I would expect "xor" to return true if there are an odd number of
> trues, and false if there are an even number of trues. It's not clear
> to me what you're asking for.
>
>
>
> --
> https://mail.python.org/mailman/listinfo/python-list

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On Tue, 14 Nov 2023 at 10:00, Dom Grigonis via Python-list
<python-list@python.org> wrote:
>
> I am not asking. Just inquiring if the function that I described could be useful for more people.
>
> Which is: a function with API that of `all` and `any` and returns `True` if specified number of elements is True.
>
> It is not a generalised `xor` in strict programatic space. I.e. NOT bitwise xor applied to many bits.
> This is more in line with cases that `any` and `all` builtins are used.
>

A generalization of XOR is exactly what Grant and I said, though: a
parity check. See for example:

https://en.wikipedia.org/wiki/Exclusive_or
https://reference.wolfram.com/language/ref/Xor.html

It tells you whether you have an odd or even number of true values.

Now, if you want something that short-circuits a counting function,
that's definitely doable, but it's a sum-and-compare, not xor. Also,
it's quite specialized so it's unlikely to end up in the stdlib.

ChrisA
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I am not arguing that it is a generalised xor.

I don’t want anything, I am just gauging if it is specialised or if there is a need for it. So just thought could suggest it as I have encountered such need several times already.

It is fairly clear by now that it is not a common one given it took some time to even convey what I mean. Bad naming didn’t help ofc, but if it was something that is needed I think it would have clicked much faster.

Thanks,
DG

> On 14 Nov 2023, at 01:12, Chris Angelico via Python-list <python-list@python.org> wrote:
>
> On Tue, 14 Nov 2023 at 10:00, Dom Grigonis via Python-list
> <python-list@python.org> wrote:
>>
>> I am not asking. Just inquiring if the function that I described could be useful for more people.
>>
>> Which is: a function with API that of `all` and `any` and returns `True` if specified number of elements is True.
>>
>> It is not a generalised `xor` in strict programatic space. I.e. NOT bitwise xor applied to many bits.
>> This is more in line with cases that `any` and `all` builtins are used.
>>
>
> A generalization of XOR is exactly what Grant and I said, though: a
> parity check. See for example:
>
> https://en.wikipedia.org/wiki/Exclusive_or
> https://reference.wolfram.com/language/ref/Xor.html
>
> It tells you whether you have an odd or even number of true values.
>
> Now, if you want something that short-circuits a counting function,
> that's definitely doable, but it's a sum-and-compare, not xor. Also,
> it's quite specialized so it's unlikely to end up in the stdlib.
>
> ChrisA
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On 2023-11-13, Dom Grigonis via Python-list <python-list@python.org> wrote:

> I am not asking. Just inquiring if the function that I described
> could be useful for more people.
>
> Which is: a function with API that of `all` and `any` and returns
> `True` if specified number of elements is True.

I've got no objection to a function that counts True objects returned
by an iterator and returns True IFF count == <N>.

I've got no objection to a function that counts True objects returned
by an iterator and returns True IFF count >= <N>.

I've got no objection if that latter function short-circuits by
stopping the iteration and returning True when it has seen <N> true
objects.

I don't recall ever having a need for such a function in the 25 years
I've been writing Python code, but I'm not going to claim that nobody
else has a need for such a function.

I would object to that being called 'xor', and would fight to the
death (yes, I'm being hyperbolic) the addition of a builtin with the
name 'xor' that does what you describe.

> It is not a generalised `xor` in strict programatic space.

AFAICT, it's not nothing at all to do with 'xor' in any sense.

> I.e. NOT bitwise xor applied to many bits. This is more in line
> with cases that `any` and `all` builtins are used.

Except the 'any' and 'all' builtins are _exactly_ the same as bitwise
or and and applided to many bits. To do something "in line" with that
using the 'xor' operator would return True for an odd number of True
values and False for an even Number of True values.

--
Grant
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> Except the 'any' and 'all' builtins are _exactly_ the same as bitwise
> or and and applided to many bits. To do something "in line" with that
> using the 'xor' operator would return True for an odd number of True
> values and False for an even Number of True values.

Fair point.

Have you ever encountered the need for xor for many bits (the one that I am NOT referring to)? Would be interested in what sort of case it could be useful.
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On 11/13/23 16:24, Dom Grigonis via Python-list wrote:
> I am not arguing that it is a generalised xor.
>
> I don’t want anything, I am just gauging if it is specialised or if there is a need for it. So just thought could suggest it as I have encountered such need several times already.
>
> It is fairly clear by now that it is not a common one given it took some time to even convey what I mean. Bad naming didn’t help ofc, but if it was something that is needed I think it would have clicked much faster.

There are things that If You Need Them You Know, and If You Do Not You
Do Not Understand - and you seem to have found one. The problem is that
forums like this are not a statistically great sampling mechanism - a
few dozen people, perhaps, chime in on many topics; there are millions
of people using Python. Still, the folks here like to think they're at
least somewhat representative :)

Hardware and software people may have somewhat different views of xor,
so *maybe* the topic title added a bit to the muddle. To me (one of
those millions), any/all falsy, any/all truthy have some interest, and
Python does provide those. Once you get into How Many True question -
whether that's the odd-is-true, even-is-false model, or the
bail-after-X-truthy-values model, it's not terribly interesting to me:
once it gets more complex than an all/any decision, I need to check for
particular combinations specifically. Two-of-six means nothing to me
until I know which combination of two it is.


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>AFAICT, it's not nothing at all to do with 'xor' in any sense.

As much as I agree that the function needn't be in the base of python, I
can easily follow the OP's logic on the function name.

With two items in the iterator, it is a standard binary exclusive or.

It is true if one of but not both of the items is true.

OP then generalized this to is exclusively one of any number of these
options are true, which is different than the repetitious binary operator
application, certainly, but is still very much an 'or' that excludes the
case of other options being true.

OP then generalized this from exclusively one truth in the set of variables
to some other specific number of truths that need be.

I expect the OP could then generalize this to a range of truthiness for the
set with a minimum and maximum allowable truthiness, and probably a key
function to extract some facet from the iterable for consideration.

I understand why you find it disagreeable, but I cannot find it necessarily
illogical, and it is easy, I think, to see what it has to do with xor.

A better name for OP's generalization, however, could likely be 'aut', from
the Latin exclusive or.


On Mon, Nov 13, 2023 at 7:20?PM Grant Edwards via Python-list <
python-list@python.org> wrote:

> On 2023-11-13, Dom Grigonis via Python-list <python-list@python.org>
> wrote:
>
> > I am not asking. Just inquiring if the function that I described
> > could be useful for more people.
> >
> > Which is: a function with API that of `all` and `any` and returns
> > `True` if specified number of elements is True.
>
> I've got no objection to a function that counts True objects returned
> by an iterator and returns True IFF count == <N>.
>
> I've got no objection to a function that counts True objects returned
> by an iterator and returns True IFF count >= <N>.
>
> I've got no objection if that latter function short-circuits by
> stopping the iteration and returning True when it has seen <N> true
> objects.
>
> I don't recall ever having a need for such a function in the 25 years
> I've been writing Python code, but I'm not going to claim that nobody
> else has a need for such a function.
>
> I would object to that being called 'xor', and would fight to the
> death (yes, I'm being hyperbolic) the addition of a builtin with the
> name 'xor' that does what you describe.
>
> > It is not a generalised `xor` in strict programatic space.
>
> AFAICT, it's not nothing at all to do with 'xor' in any sense.
>
> > I.e. NOT bitwise xor applied to many bits. This is more in line
> > with cases that `any` and `all` builtins are used.
>
> Except the 'any' and 'all' builtins are _exactly_ the same as bitwise
> or and and applided to many bits. To do something "in line" with that
> using the 'xor' operator would return True for an odd number of True
> values and False for an even Number of True values.
>
> --
> Grant
> --
> https://mail.python.org/mailman/listinfo/python-list
>
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On Tue, 14 Nov 2023 at 11:29, Dom Grigonis via Python-list
<python-list@python.org> wrote:
>
>
> > Except the 'any' and 'all' builtins are _exactly_ the same as bitwise
> > or and and applided to many bits. To do something "in line" with that
> > using the 'xor' operator would return True for an odd number of True
> > values and False for an even Number of True values.
>
> Fair point.
>
> Have you ever encountered the need for xor for many bits (the one that I am NOT referring to)? Would be interested in what sort of case it could be useful.

Yes, parity checking. That's why I namedropped that in my prior
response - it's an easy thing to search the web for if you want to
know more about it.

Here's a couple of excellent videos on error correction, and you'll
see XOR showing up as a crucial feature:

https://www.youtube.com/watch?v=X8jsijhllIA
https://www.youtube.com/watch?v=h0jloehRKas

ChrisA
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I agree, from perspective of standard `all` and `any` use cases this does not seem very useful.

However, in my experience it has its usages. E.g.:
* If sum(map(bool, iterable) [> | <] n can be useful. Counting dead processes and similar, optimisation problems where need to re-initialise if less than certain number of nodes reached certain threshold.
* If sum(map(bool, iterable) [== | !=] n is an edge case. Can’t even think of an example
* Finally, it would be a convenient shorthand for `bool(a) ^ bool(b)`

I sometimes think that there is also a case when certain function is not in one’s mind he doesn’t see the usefulness, but sometimes the sheer knowledge of its existence can twist certain situations in a positive manner.

What about an alternative, which does seem more useful:

def count_compare(iterable, n):
return np.sign(sum(map(bool, iterable)) - n)

print(count_compare([False, False, False], 1))
As I am here, I will dare to ask if there is no way that `sign` function is going to be added to `math` or `builtins`. `np.sign` does the trick, but it is very slow to be used on a single number. And yes, I know that `copysign` exists, it just doesn’t do the same thing.

DG

> On 14 Nov 2023, at 02:33, Mats Wichmann via Python-list <python-list@python.org> wrote:
>
> On 11/13/23 16:24, Dom Grigonis via Python-list wrote:
>> I am not arguing that it is a generalised xor.
>> I don’t want anything, I am just gauging if it is specialised or if there is a need for it. So just thought could suggest it as I have encountered such need several times already.
>> It is fairly clear by now that it is not a common one given it took some time to even convey what I mean. Bad naming didn’t help ofc, but if it was something that is needed I think it would have clicked much faster.
>
> There are things that If You Need Them You Know, and If You Do Not You Do Not Understand - and you seem to have found one. The problem is that forums like this are not a statistically great sampling mechanism - a few dozen people, perhaps, chime in on many topics; there are millions of people using Python. Still, the folks here like to think they're at least somewhat representative :)
>
> Hardware and software people may have somewhat different views of xor, so *maybe* the topic title added a bit to the muddle. To me (one of those millions), any/all falsy, any/all truthy have some interest, and Python does provide those. Once you get into How Many True question - whether that's the odd-is-true, even-is-false model, or the bail-after-X-truthy-values model, it's not terribly interesting to me: once it gets more complex than an all/any decision, I need to check for particular combinations specifically. Two-of-six means nothing to me until I know which combination of two it is.
>
>
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> https://mail.python.org/mailman/listinfo/python-list

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On Tue, 14 Nov 2023 at 12:02, Dom Grigonis via Python-list
<python-list@python.org> wrote:
> As I am here, I will dare to ask if there is no way that `sign` function is going to be added to `math` or `builtins`.
>

https://docs.python.org/3/library/math.html#math.copysign

ChrisA
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On 14/11/2023 00:33, Mats Wichmann via Python-list wrote:
> Hardware and software people may have somewhat different views of xor

I've come at it from both sides. I started life as a telecomms
technician and we learned about xor in the context of switching
and relays and xor was a wiring configuration for scenarios where
you wanted any single change of switch state to toggle the
entire system (think a stairwell with switches on every
landing).

Later, I got into software engineering and we studied Boolean
algebra and xor was an odd number of Truth values, used in
parity tests (and in encryption).

But from both perspectives xor is pretty clearly defined
in how it operates and not, I suspect, what the OP really
wants in this case.

--
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Author of the Learn to Program web site
http://www.alan-g.me.uk/
http://www.amazon.com/author/alan_gauld
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http://www.flickr.com/photos/alangauldphotos


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On Tue, 14 Nov 2023 at 11:40, Chris Angelico <rosuav@gmail.com> wrote:
> Here's a couple of excellent videos on error correction, and you'll
> see XOR showing up as a crucial feature:
>
> https://www.youtube.com/watch?v=X8jsijhllIA
> https://www.youtube.com/watch?v=h0jloehRKas
>

I just flipped through that 3blue1brown video again, and as it turns
out, the actual part where he talks about multi-argument XOR happens
in part two (it's barely touched on at the very end as he's
introducing part two).

https://www.youtube.com/watch?v=b3NxrZOu_CE

Honestly though, the full video is well worth watching. More modern
error correction systems are slightly different, but will still be
built on many of the same principles.

ChrisA
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On 2023-11-14, Dom Grigonis via Python-list <python-list@python.org> wrote:
>
>> Except the 'any' and 'all' builtins are _exactly_ the same as bitwise
>> or and and applided to many bits. To do something "in line" with that
>> using the 'xor' operator would return True for an odd number of True
>> values and False for an even Number of True values.
>
> Fair point.
>
> Have you ever encountered the need for xor for many bits (the one
> that I am NOT referring to)? Would be interested in what sort of
> case it could be useful.

Yes, it's used all the time in low-level communications protocols,
where it's often implemented in hardware. But, it is also not at all
unusual to implement it in software.

It's also not that unusual for the "count-ones" part of the function
you're asking for to be implemented in hardware by a CPU having an
instruction that counts the number of 1 bits in a register.

GCC has a low-level builtins called __builtin_popcount() and
__builtin-popcountl() that counts the number of 1's in an unsigned
(long) int.


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I was going to ask a dumb question. Has any other language you know of made
something available that does what is being asked for and included it in the
main program environment rather than an add-on?

A secondary mention here has been whether short-circuiting functions like
"any" and "all" have been augmented with something like "has_n" that
evaluates arguments till it has found n or perhaps n+1 of what it wants then
skips the rest. Does any language supply something like that? What would
such a function return and does it have an "any" or an "all" side?

It sounds like if I asked if a list of integers has at least n prime numbers
in "any" mode, it should ignore any that are not primes till it finds n
primes or fails and returns true or false. If in "all" mode, I assume it
would have to be the first n items without a failure.

Fine, but then someone may want to know WHERE you stopped or for you to
return the sublist of the ones that made the match, or even return
everything that was skipped so you can later process that. Consider a long
list of jurors you process to place a dozen that qualify on a jury and then
later you want to choose from among the rest for another jury.

Human minds can come up with an amazing number of ideas including for
"useful" functions or features but I find the vast majority would rarely be
used as nobody remembers it is available and some fairly simple method using
other functions can easily be cobbled together.

-----Original Message-----
From: Python-list <python-list-bounces+avi.e.gross=gmail.com@python.org> On
Behalf Of Grant Edwards via Python-list
Sent: Monday, November 13, 2023 8:19 PM
To: python-list@python.org
Subject: Re: xor operator

On 2023-11-14, Dom Grigonis via Python-list <python-list@python.org> wrote:
>
>> Except the 'any' and 'all' builtins are _exactly_ the same as bitwise
>> or and and applided to many bits. To do something "in line" with that
>> using the 'xor' operator would return True for an odd number of True
>> values and False for an even Number of True values.
>
> Fair point.
>
> Have you ever encountered the need for xor for many bits (the one
> that I am NOT referring to)? Would be interested in what sort of
> case it could be useful.

Yes, it's used all the time in low-level communications protocols,
where it's often implemented in hardware. But, it is also not at all
unusual to implement it in software.

It's also not that unusual for the "count-ones" part of the function
you're asking for to be implemented in hardware by a CPU having an
instruction that counts the number of 1 bits in a register.

GCC has a low-level builtins called __builtin_popcount() and
__builtin-popcountl() that counts the number of 1's in an unsigned
(long) int.


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