%f format behaves incorrectly

Question

%f format behaves incorrectly

josevalim opened this issue 5 years ago · comments

Different to other formats, the padding on %f should be a trailing pad. For example, this:

NimbleStrftime.format(~U"2019-08-15 17:07:57.001Z", "%I:%M:%S.%f %p")

is formatted as:

"05:07:57.1000 PM"

which is not correct. I believe by default it should be formatted using the padding in the datetime struct (which is the second element of the microsecond field).

So ~U"2019-08-15 17:07:57.001Z" should be padded as 57.001 but ~U"2019-08-15 17:07:57.001000Z" should be padded as 57.001000. The user can force a particular padding but I think in this case it will be more like a precision rather than padding. So if I say the "padding" is 1, we will only ever show the first digit.

How do other strftime implementations behave here?

José Valim commented 5 years ago

Correct!

Gustavo · Answer 1 · Mon Aug 26 2019 22:26:20 GMT+0800 (China Standard Time)

Python and Haskell are the only ones I found with the %f format so far, Python does not accept padding or width options for it and Haskell uses it for century instead of microseconds
Also tried looking at C, C++, C#, Ruby, PHP and Perl

José Valim · Answer 2 · Mon Aug 26 2019 23:31:03 GMT+0800 (China Standard Time)

And how does Python behave here?

Gustavo · Answer 3 · Tue Aug 27 2019 00:04:19 GMT+0800 (China Standard Time)

it ignores the format and treats it as a non format part of the string
example

>>> import time
>>> t = (2009, 2, 17, 17, 3, 38, 1, 48, 0)
>>> t = time.mktime(t)
>>> print time.strftime("%b %d %Y %H:%M:%S.%_2f", time.gmtime(t))
Feb 17 2009 20:03:38.%_2f

José Valim · Answer 4 · Tue Aug 27 2019 00:06:27 GMT+0800 (China Standard Time)

So let’s ignore those for %f. We will always format it according to the precision in the DateTime. Also, we should probably behave like Python and ignore the format if pad/width is given to a format that does not support those. -- *José Valimwww.plataformatec.com.br <http://www.plataformatec.com.br/>Founder and Director of R&D*

Gustavo · Answer 5 · Tue Aug 27 2019 00:29:11 GMT+0800 (China Standard Time)

I tested all accepted formats in python(at least all documented here) and only %f behaves like that, all others accept padding and width normally

José Valim · Answer 6 · Tue Aug 27 2019 00:29:35 GMT+0800 (China Standard Time)

Interesting, thanks!

Gustavo · Answer 7 · Tue Aug 27 2019 02:33:32 GMT+0800 (China Standard Time)

so just to be sure if I understand what to do, if a width and a pad are received with the microsecond option we ignore them and do the default formatting based on precision, right?