Alexander Belopolsky belopolsky@users.sourceforge.net added the comment:

I wonder if this is subject to change. I find it odd that

...

...

"{:g}".format(1e3)

'1000'

but one has to use % in

...

...

"{:%Y}".format(datetime.now())

'2010'

It is also different from PEP 3101 recommendation: """ An example is the 'datetime' class, whose format specifiers might look something like the arguments to the strftime() function:

"Today is: {0:a b d H:M:S Y}".format(datetime.now()) """ The above, however, should probably be

"Today is: {0:a} {0:b} {0:d} {0:H}:{0:M}:{0:S} {0:Y}".format(datetime.now())

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Eric Smith eric@trueblade.com added the comment:

I think Alexander's example is best written as: "Today is: {0:%a %b %d %H:%M:%S %Y}".format(datetime.now())

I agree with Brett that there's nothing unusual about having type-specific formatting languages, and for datetime strftime is the obvious choice. It's a little unfortunate that % is used, as it's mildly confusing with %-formatting, but not much can be done with that issue.

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Alexander Belopolsky belopolsky@users.sourceforge.net added the comment:

The problem I have with strftime %-format codes is that according to BSD manual page they have already ran out of English alphabet and still "there is no conversion specification for the phase of the moon." :-)

On a serious note, there are no codes to format TZ offset hours and minutes separately which precludes specifying an important RFC 3339 format.

I think we should take this opportunity to define a comprehensive mini-language for datetime formatting rather than slavishly reuse strftime.

The new mini-language may end up to be a superset of that for strftime, but I would rather not commit to supporting %-codes indefinitely.

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Éric Araujo merwok@netwok.org added the comment:

I think this particular wheel has one very good reinvention as the Locale Data Markup Language specification. Example from the Python Babel package:

...

...

format_datetime(dt, "yyyyy.MMMM.dd GGG hh:mm a", locale='en')

u'02007.April.01 AD 03:30 PM'

http://unicode.org/reports/tr35/#Date_Format_Patterns http://babel.edgewall.org/wiki/Documentation/dates.html#pattern-syntax

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R. David Murray rdmurray@bitdance.com added the comment:

Alexander closed issue 7789 in favor of this one, which is fine, but I want to respond to Eric's rejection there of including info about datetime in the 'format mini language' section of the docs. His point was that only the builtin types were documented there, but if the goal is to get people to actually use this facility, it would be helpful if some mention were made there of other stdlib types that support __format__. Some set of 'see also' links, perhaps in a footnote?

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Changes by Florent Xicluna florent.xicluna@gmail.com:

---------- type: -> behavior versions: +Python 3.3 -Python 2.6, Python 3.1

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Heikki Partanen added the comment:

Added documentation for __format__ for datetime, time and date, and also added example code for using string.format. Seemed to merge cleanly to 3.4 and 2.7.

---------- keywords: +patch nosy: +heikki.partanen Added file: http://bugs.python.org/file27684/issue8913.patch

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Changes by Andrew Svetlov andrew.svetlov@gmail.com:

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Heikki Partanen added the comment:

Thanks for the comments, Eric!

I reworded the docs and improved the examples too (being stuck in 2.6 I didn't even know about the cool autonumbering :)

---------- Added file: http://bugs.python.org/file27782/issue8913-2.patch

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Eric V. Smith added the comment:

To Heikki Partanen excellent point in the review about date __format__ strings allowing you to combine date formatting with other types of formatting:

This is a great point. It's the lack of this that (for example) requires the logging module to have a separate datefmt parameter. With %-formatting, there's no easy way to say:

'{timestamp:%Y%m%d-%H%M%S} {hostname:^40} {count:02d}'.format(timestamp=ts, hostname=host, count=count)

That is, with %-formatting you can't have a single string that specifies both a date/time format and other formatting as well as other formatting specifiers.

I don't think the example in the patch is great, but I do think that it's a good point that needs to be emphasized.

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Éric Araujo added the comment:

Ezio, you are the latest reviewer, do you have outstanding comments?

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Heikki Partanen added the comment:

Improved the datetime example to have time part

---------- Added file: http://bugs.python.org/file29663/issue8913-4.patch

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Ezio Melotti added the comment:

I left another review with a couple of suggestions. The patch is OK, it's just that the examples look a bit meaningless to me.

---------- stage: -> patch review versions: +Python 3.4 -Python 3.2

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Roundup Robot added the comment:

New changeset 40f582a73901 by Ezio Melotti in branch '3.3': #8913: add examples and docs for date/time/datetime.__format__. Patch by Heikki Partanen. http://hg.python.org/cpython/rev/40f582a73901

New changeset 8dd7f7134700 by Ezio Melotti in branch 'default': #8913: merge with 3.3. http://hg.python.org/cpython/rev/8dd7f7134700

New changeset 0dac103a41bb by Ezio Melotti in branch '2.7': #8913: add examples and docs for date/time/datetime.__format__. Patch by Heikki Partanen. http://hg.python.org/cpython/rev/0dac103a41bb

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