Re: [Python-Dev] Why is nb_inplace_power ternary?
The same way += et al. are in-place: it would ask 'x' to modify itself, if it can. If not, no harm done. (It would be called as 'x = ipow(x, n, 10)' of course, just like 'x += n' is really 'x = x.__iadd__(n)') On 2/10/07, Martin v. Löwis [EMAIL PROTECTED] wrote: Greg Ewing schrieb: What could the syntax for that be? It wouldn't be a syntax, just a function, e.g. ipow(x, n, 10) In what way would that be inplace? A function cannot rebind the variables it gets as parameters. Regards, Martin ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/thomas%40python.org -- Thomas Wouters [EMAIL PROTECTED] Hi! I'm a .signature virus! copy me into your .signature file to help me spread! ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
Thomas Wouters schrieb: The same way += et al. are in-place: it would ask 'x' to modify itself, if it can. If not, no harm done. (It would be called as 'x = ipow(x, n, 10)' of course, just like 'x += n' is really 'x = x.__iadd__(n)') I think this would violate the policy that a mutating function shouldn't give the object being modified as the result - just as list.reverse doesn't return the list, in addition to reversing it in-place. Regards, Martin ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
Sure, and I don't know if anyone will ever want ipow() -- but I've never seen real code use the three-argument pow() either. The fact is that all the in-place modifying hooks return the result (which may or may not be self, and may or may not be mutated) so an in-place three-argument pow() would have to do the same. I would prefer keeping the similarity between __ipow__ and __pow__, although I don't care if that means keeping the always-unused third argument to __ipow__ (which isn't really in the way, after all) or adding a new hook for the three-argument pow(). On 2/14/07, Martin v. Löwis [EMAIL PROTECTED] wrote: Thomas Wouters schrieb: The same way += et al. are in-place: it would ask 'x' to modify itself, if it can. If not, no harm done. (It would be called as 'x = ipow(x, n, 10)' of course, just like 'x += n' is really 'x = x.__iadd__(n)') I think this would violate the policy that a mutating function shouldn't give the object being modified as the result - just as list.reverse doesn't return the list, in addition to reversing it in-place. Regards, Martin -- Thomas Wouters [EMAIL PROTECTED] Hi! I'm a .signature virus! copy me into your .signature file to help me spread! ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
Martin v. Löwis wrote: I think this would violate the policy that a mutating function shouldn't give the object being modified as the result Well, it's a necessary violation, given the way the inplace methods work. And it doesn't *necessarily* return the same value, it might return a new object. So the return value conveys useful information, unlike with list.sort() et al. -- Greg ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
Greg Ewing schrieb: What could the syntax for that be? It wouldn't be a syntax, just a function, e.g. ipow(x, n, 10) In what way would that be inplace? A function cannot rebind the variables it gets as parameters. Regards, Martin ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
Jim Jewett schrieb: Either x**= n % 10 # The **= changes the parse context, so that % is no longer # immediately evaluated Are you seriously proposing such a change? I was asking for spellings that currently don't have a meaning (rather, I was suggesting that no such spelling exists, and the entire idea of supporting such notation in the language is ridiculous). x**= (n, 10) # exponentiation to a tuple isn't currently defined, and it Likewise: it currenly is well-defined: it invoked nb_inplace_power with the tuple (and __ipow__ if x's class is written in Python). Whether this gives a TypeError or not depends on the class of x. Regards, Martin ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
Brett Cannon schrieb: Seems reasonable to me. Is the argument of None passed in automatically somewhere? There are few callers of nb_inplace_power at all (AFAICT, only PyNumber_InPlacePower); in turn, PyNumber_InPlacePower is called with the implicit Py_None always: - ceval.c, for INPLACE_POWER (which is binary) - operator.ipow (which is also binary) - class.c, from bin_inplace_power, which in turn is called from instance_ipow if the instance's 3rd argument to nb_inplace_power is Py_None (if there is a non-None third argument, instance_ipow invokes __ipow__ with three arguments if __ipow__ is defined, else it invokes __pow__ with three arguments) The only case I could find where a third argument is non-None is when the builtin pow() is invoked, which then invokes nb_power (but not nb_inplace_power) with three arguments. Regards, Martin ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
Raymond Hettinger schrieb: That made sense, but my question was whether there would be benefit to making the change in the middle of a major release. At worst, code that is currently working due to undefined behavior will stop working. I don't see any offsetting benefit. ISTM that Py2.5 should be left as-is and that the full signature change be made in Py2.6. I can't see left as is as an option, see #1648268 and #1653736. Apparently, there are platforms where the code traps when there is a signature mismatch. If raising an exception is unacceptable, I'd rather explicitly ignore the extra argument, instead of ignoring it implicitly. Regards, Martin ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
Greg Ewing schrieb: Might we want to add an in-place version of the 3-arg pow() function one day? If so, leaving the third argument there could be useful. What could the syntax for that be? Instead of writing x = pow(x, n, 10) would you write x pow n = 10 ? or perhaps x ** n = 10 or x * n *= 10 Also, it would break existing __ipow__ implementations that only receive two arguments (unless there would be another __ method introduced). Regards, Martin ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
[Python-Dev] Why is nb_inplace_power ternary?
Greg Ewing schrieb: Might we want to add an in-place version of the 3-arg pow() function one day? If so, leaving the third argument there could be useful. Martin v. Löwis martin at v.loewis.de replied: What could the syntax for that be? Instead of writing x = pow(x, n, 10) Either x**= n % 10 # The **= changes the parse context, so that % is no longer # immediately evaluated or x**= (n, 10) # exponentiation to a tuple isn't currently defined, and it # does show that both arguments are part of the power # expression -- but I'm not sure it needs a 3-argument form # instead of just unpacking the tuple itself. -jJ ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
On 2/9/07, Martin v. Löwis [EMAIL PROTECTED] wrote: Brett Cannon schrieb: Seems reasonable to me. Is the argument of None passed in automatically somewhere? There are few callers of nb_inplace_power at all (AFAICT, only PyNumber_InPlacePower); in turn, PyNumber_InPlacePower is called with the implicit Py_None always: - ceval.c, for INPLACE_POWER (which is binary) - operator.ipow (which is also binary) - class.c, from bin_inplace_power, which in turn is called from instance_ipow if the instance's 3rd argument to nb_inplace_power is Py_None (if there is a non-None third argument, instance_ipow invokes __ipow__ with three arguments if __ipow__ is defined, else it invokes __pow__ with three arguments) The only case I could find where a third argument is non-None is when the builtin pow() is invoked, which then invokes nb_power (but not nb_inplace_power) with three arguments. Well then explicitly ignoring the object makes sense to me. While I am personally fine with raising the exception, erring on the side of caution as Raymond is suggesting wouldn't hurt either. -Brett ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
Martin v. Löwis wrote: Greg Ewing schrieb: Might we want to add an in-place version of the 3-arg pow() function one day? What could the syntax for that be? It wouldn't be a syntax, just a function, e.g. ipow(x, n, 10) Also, it would break existing __ipow__ implementations that only receive two arguments You could consider them broken already, since the signature clearly implies that there could be a third argument. The fact that it's not currently used is no excuse. :-) -- Greg ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
[Python-Dev] Why is nb_inplace_power ternary?
#1653736 reports that slot_nb_inplace_power has the wrong type: it should be a ternary function, but only is a binary. The proposed change is to make it ternary, and to invoke __ipow__ with three arguments. In researching this, I came to wonder why nb_inplace_power is ternary in the first place. It is the implementation of foo **= bar (and that's its only use), so it ought to be binary. Historically, the reason probably is that it was copied from nb_power, which is ternary because it also implements pow()). So here is my proposed change: 1. For 2.5.1, rewrite slot_nb_inplace_power to raise an exception if the third argument is not None, and then invoke __ipow__ with only one argument. 2. For 2.6, change the API to make nb_inplace_power binary. Optionally, in 2.5, the exception could be added into other places as well, e.g. PyNumber_InPlacePower and instance_ipow (rather than invoking __ipow__ with a third argument if its not None). Comments? Regards, Martin ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
[MvL] So here is my proposed change: 1. For 2.5.1, rewrite slot_nb_inplace_power to raise an exception if the third argument is not None, and then invoke __ipow__ with only one argument. Why would you change Py2.5? There is no bug here. Raymond ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
[EMAIL PROTECTED] schrieb: 1. For 2.5.1, rewrite slot_nb_inplace_power to raise an exception if the third argument is not None, and then invoke __ipow__ with only one argument. Why would you change Py2.5? There is no bug here. There is: slot_nb_inplace has the signature static PyObject * slot_nb_inplace_power(PyObject *self, PyObject * arg1) yet it is stored in as_number.nb_inplace_power, which is defined as typedef PyObject * (*ternaryfunc)(PyObject *, PyObject *, PyObject *); ternaryfunc nb_inplace_power; This has undefined behavior. Even if it had, slot_nb_inplace_power would silently discard its third argument. Regards, Martin ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
On 2/8/07, Martin v. Löwis [EMAIL PROTECTED] wrote: #1653736 reports that slot_nb_inplace_power has the wrong type: it should be a ternary function, but only is a binary. The proposed change is to make it ternary, and to invoke __ipow__ with three arguments. In researching this, I came to wonder why nb_inplace_power is ternary in the first place. It is the implementation of foo **= bar (and that's its only use), so it ought to be binary. Historically, the reason probably is that it was copied from nb_power, which is ternary because it also implements pow()). So here is my proposed change: 1. For 2.5.1, rewrite slot_nb_inplace_power to raise an exception if the third argument is not None, and then invoke __ipow__ with only one argument. 2. For 2.6, change the API to make nb_inplace_power binary. Optionally, in 2.5, the exception could be added into other places as well, e.g. PyNumber_InPlacePower and instance_ipow (rather than invoking __ipow__ with a third argument if its not None). Comments? Seems reasonable to me. Is the argument of None passed in automatically somewhere? I think the 2.6 change is definitely good, just don't know if the exception is really needed. I realize the signature is off, but it doesn't hurt anyone at this point if it stayed wrong since obviously the semantics would be the same as they were. -Brett ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
Martin v. Löwis wrote: It is the implementation of foo **= bar (and that's its only use), so it ought to be binary. Maybe it's so that a type can plug the same implementation into both nb_pow and nb_inplace_pow. Although the same effect could be achieved by just leaving nb_inplace_pow null, so I suppose that's not necessary. Might we want to add an in-place version of the 3-arg pow() function one day? If so, leaving the third argument there could be useful. -- Greg ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
Re: [Python-Dev] Why is nb_inplace_power ternary?
[MvL] 1. For 2.5.1, rewrite slot_nb_inplace_power to raise an exception if the third argument is not None, and then invoke __ipow__ with only one argument. [Raymond] Why would you change Py2.5? There is no bug here. [MvL] There is: slot_nb_inplace has the signature static PyObject * slot_nb_inplace_power(PyObject *self, PyObject * arg1) yet it is stored in as_number.nb_inplace_power, which is defined as typedef PyObject * (*ternaryfunc)(PyObject *, PyObject *, PyObject *); ternaryfunc nb_inplace_power; This has undefined behavior. Even if it had, slot_nb_inplace_power would silently discard its third argument. That made sense, but my question was whether there would be benefit to making the change in the middle of a major release. At worst, code that is currently working due to undefined behavior will stop working. I don't see any offsetting benefit. ISTM that Py2.5 should be left as-is and that the full signature change be made in Py2.6. Raymond ___ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
