id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
16906	Avoid strftime when isoformat can do the job	Aymeric Augustin	nobody	"While working on timezone support in Django, the inconsistency in these three functions surprised me: https://code.djangoproject.com/browser/django/trunk/django/db/backends/__init__.py#L714

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In fact, r7946 introduced a `datetime_safe` module that provides a Python implementation of `datetime.[date|datetime].strftime` for dates before 1900.

However, this is overkill for the purpose of just showing a `date` or `datetime` in ISO format (`%Y-%m-%d` and `%Y-%m-%d %H:%M:%S`). It makes the code needlessly complicated, sometimes inconistent, and inefficient. The `isoformat` method achieves the same result, works for any date, and is implemented in C.

Also, some code still uses the `strftime` function from the standard library. Using `isoformat` is better because it isn't subject to the 1900 limit.

See attached patch.

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For more background, see `isoformat_date` in http://svn.python.org/view/python/tags/r271/Modules/datetimemodule.c?view=markup. Note that `date` objects have no `__unicode__` and their `__str__` just call `isoformat`, so `str(date)` or `unicode(date)` is the same as `datetime_safe.date(date.year, date.month, date.day).strftime('%Y-%m-%d')`. It's pretty much the same for `datetime` objects, except that `isoformat` uses `T` as a separator, while `str` and `unicode` use a space.

Changing `date.format('%Y-%m-%d')` to `date.isoformat()` is safe. Changing `datetime.format('%Y-%m-%d %H:%M:%S')` to `datetime.isoformat()` requires removing the microseconds and the timezone first, if there is one, so the correct pattern is `datetime.replace(microsecond=0, tzinfo=None)`. This also applies for time objects.
"	Cleanup/optimization	closed	Core (Other)	1.3	Normal	fixed			Ready for checkin	0	0	0	0	0	0