[issue19933] Round default argument for ndigits
Roundup Robot added the comment: New changeset e3cc75b1000b by Steve Dower in branch 'default': Issue 19933: Provide default argument for ndigits in round. Patch by Vajrasky Kok. https://hg.python.org/cpython/rev/e3cc75b1000b -- nosy: +python-dev ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Changes by Steve Dower steve.do...@microsoft.com: -- resolution: - fixed status: open - closed versions: +Python 3.5 -Python 3.4 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Terry J. Reedy added the comment:
The docstring is better than the current doc as it says that the default
precision is 0, without calling that the default for ndigits.
''' round(number[, ndigits]) - number
Round a number to a given precision in decimal digits (default 0 digits).
This returns an int when called with one argument, otherwise the
same type as the number. ndigits may be negative.'''
---
Sidenote: To write round in Python, one could easily write
_sentinel = object
def round(number, ndigits=_sentinel):
if ndigits is _sentinel: ...
which makes ndigits positional-or-keyword, and almost optional-with-no-default,
as _sentinel is close enough to being a default that cannot be passed in. This
is a standard idiom. One who was really picky about having no default could use
def round(number, *args, **kwds): ...
and look for len(args) == 1 xor kwds.keys() == {'ndigits'}.
--
nosy: +terry.reedy
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[issue19933] Round default argument for ndigits
Mark Dickinson added the comment: After patch: round(1.23, 0) = 1 not 1.0 round(4.67, 0) = 5 not 5.0 Please no! Two-argument round should continue to return a float in all cases. The docs should be fixed. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Mark Dickinson added the comment: But also there should be a way to make round return an integer I don't understand. There's already a way to make round return an integer: don't pass a second argument. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Changes by Vajrasky Kok sky@speaklikeaking.com: Added file: http://bugs.python.org/file33053/fix_doc_round_ndigits.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Vajrasky Kok added the comment: Okay, here is the patch to fix the doc. -- Added file: http://bugs.python.org/file33052/fix_doc_round_ndigits.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Changes by Vajrasky Kok sky@speaklikeaking.com: Removed file: http://bugs.python.org/file33052/fix_doc_round_ndigits.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Changes by Vajrasky Kok sky@speaklikeaking.com: Removed file: http://bugs.python.org/file33053/fix_doc_round_ndigits.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Changes by Vajrasky Kok sky@speaklikeaking.com: Added file: http://bugs.python.org/file33054/fix_doc_round_ndigits.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Mark Dickinson added the comment: Thanks. It's inaccurate to say that a float is returned in general, though: for most builtin numeric types, what's returned has the same type as its input. So rounding a Decimal to two places gives a Decimal on output, etc. (That's already explained in the next paragraph.) -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Mark Dickinson added the comment: How about just removing the mention of 'defaults to zero', and say something like: if ndigits is omitted, returns the nearest int to its input -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
João Bernardo added the comment: I don't understand. There's already a way to make round return an integer: don't pass a second argument. If this function were to be written in Python, it would be something like: def round(number, ndigits=0): ... or def round(number, ndigits=None): ... But in C you can forge the signature to whatever you want and parse the arguments accordingly. In Python there's always a way to get the default behavior by passing the default argument, but in C it may not exist (in this case `PyObject *o_ndigits = NULL;`) So, I propose the default value being `None`, so this behavior can be achieved using a second argument. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Vajrasky Kok added the comment: Here is the updated doc fix. Anyway, why not round(1.2) - 1.0 in the first place? Just curious. -- Added file: http://bugs.python.org/file33060/fix_doc_round_ndigits_v2.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
João Bernardo added the comment: Anyway, why not round(1.2) - 1.0 in the first place? Just curious. It was the behavior on Python 2.x, but somehow when they changed the rounding method to nearest even number this happened... I think it's too late to change back the return type. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
R. David Murray added the comment: Do you have any real-world motivating use case for None? Not just theoretical consistency with what a Python version of the function would look like. (I'm not saying we shouldn't consider supporting None as a low priority change, I'm just trying to figure out where you'd ever need it in the real world.) -- nosy: +r.david.murray ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
João Bernardo added the comment: Not really. Just consistency: For the same reason ' foo '.strip(None) works... To avoid special casing the function call when you already have a variable to hold the argument. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
R. David Murray added the comment: Right, but None in that case has real world utility, since you might have the the value in a variable. But you are hardly going to hold int-or-not in a variable, especially a variable that is really about the number of places in the float result... -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Mark Dickinson added the comment: Anyway, why not round(1.2) - 1.0 in the first place? Just curious. All this changed as part of PEP 3141. I wasn't watching Python 3 development closely back then, but I *think* at least part of the motivation was to provide a way to get away from the use of `int` to truncate a float to its integer part: the argument goes that a simple type conversion shouldn't throw away information, and that if you want a transformation from float to int that throws away information you should ask for it explicitly. So `math.trunc` was born as the preferred way to truncate a float to an int, and `math.floor`, `math.ceil` and `round` became alternative float - int conversion methods. That entailed those functions returning ints. off-topic In the case of `math.floor` and `math.ceil` at least, I think this is regrettable. There are plenty of places where you just want a float - float floor or ceiling, and Python no longer has a cheap operation for that available: floor as a float-to-float operation is cheap; floor as a float-to-long-integer operation is significantly more costly. In the case of `round`, we still have `round(x, 0)` available as a cheap float-float conversion, so it's less of a problem. And I hardly ever use `trunc`, so I don't care about that case. /off-topic -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Vajrasky Kok added the comment: In case we want to add consistency with None ndigits, here is the patch adding support for None value for ndigits parameter. This one looks like a low-risk addition but since Python 3.4 is in beta phase -- Added file: http://bugs.python.org/file33074/fix_doc_ndigits_round_and_add_None_ndigits.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
New submission from João Bernardo: From the docs for built-in function round: If ndigits is omitted, it defaults to zero (http://docs.python.org/3/library/functions.html#round) But, the only way to get an integer from `round` is by not having the second argument (ndigits): round(3.5) 4 round(3.5, 1) 3.5 round(3.5, 0) 4.0 round(3.5, -1) 0.0 round(3.5, None) Traceback (most recent call last): File pyshell#6, line 1, in module round(3.5, None) TypeError: 'NoneType' object cannot be interpreted as an integer Either the docs are wrong or the behavior is wrong. I think it's easier to fix the former... But also there should be a way to make round return an integer (e.g. passing `None` as 2nd argument) -- assignee: docs@python components: Documentation, Interpreter Core messages: 205647 nosy: JBernardo, docs@python priority: normal severity: normal status: open title: Round default argument for ndigits versions: Python 3.4 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Vajrasky Kok added the comment: Here is the preliminary patch. After patch: round(1.23, 0) = 1 not 1.0 round(4.67, 0) = 5 not 5.0 -- keywords: +patch nosy: +vajrasky Added file: http://bugs.python.org/file33051/fix_round_with_zero_ndigits.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue19933] Round default argument for ndigits
Changes by Vajrasky Kok sky@speaklikeaking.com: -- nosy: +mark.dickinson ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue19933 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
