[doc] Incorrect documentation for strftime()/strptime() format code %f

[jujuwoman]

BPO	33381
Nosy	@freddrake, @MojoVampire, @pganssle, @miss-islington, @jujuwoman, @iritkatriel, @vishalpandeyvip
PRs	bpo-33381: [doc] strftime's %f option may pad zeros on the left or the right #29801 [3.10] bpo-33381: [doc] strftime's %f option may pad zeros on the left or the right (GH-29801) #29862 [3.9] bpo-33381: [doc] strftime's %f option may pad zeros on the left or the right (GH-29801) #29863
Files	Bug description.py: MWE of the bug

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-11-30.11:51:15.436>
created_at = <Date 2018-04-29.01:06:18.507>
labels = ['easy', 'type-bug', '3.9', '3.10', '3.11', 'library', 'docs']
title = '[doc] Incorrect documentation for strftime()/strptime() format code %f'
updated_at = <Date 2021-11-30.11:51:15.435>
user = 'https://github.com/jujuwoman'

bugs.python.org fields:

activity = <Date 2021-11-30.11:51:15.435>
actor = 'iritkatriel'
assignee = 'docs@python'
closed = True
closed_date = <Date 2021-11-30.11:51:15.436>
closer = 'iritkatriel'
components = ['Documentation', 'Library (Lib)']
creation = <Date 2018-04-29.01:06:18.507>
creator = 'jujuwoman'
dependencies = []
files = ['47556']
hgrepos = []
issue_num = 33381
keywords = ['patch', 'easy', 'newcomer friendly']
message_count = 8.0
messages = ['315873', '316110', '321106', '407353', '407357', '407362', '407363', '407364']
nosy_count = 8.0
nosy_names = ['fdrake', 'docs@python', 'josh.r', 'p-ganssle', 'miss-islington', 'jujuwoman', 'iritkatriel', 'vishalpandeyvip']
pr_nums = ['29801', '29862', '29863']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue33381'
versions = ['Python 3.9', 'Python 3.10', 'Python 3.11']

[jujuwoman]

According to https://docs.python.org/3/library/datetime.html, %f is zero-padded on the left. But actual Python 3 behavior is puts the zero padding on the right.

[MojoVampire]

Note: strftime follows the existing documentation:

>>> datetime.datetime(1970, 1, 1, microsecond=1).strftime('%f')
'000001'

The strptime behavior bug seems like a duplicate of bpo-32267, which claims to be fixed in master as of early January; may not have made it into a release yet though. I can't figure out how to view the patch on that issue, it doesn't seem to be linked to GitHub like normal.

[pganssle]

I don't believe this is a duplicate if bpo-32267, which is actually about the %z directive.

I think the implementation here is correct and the documentation is semi-correct, it depends on how you look at it, consider:

>>> datetime(2018, 1, 1, 0, 0, 0, 1).strftime('%f')
'000001'

>>> datetime(2018, 1, 1, 0, 0, 0, 100000).strftime('%f')
'100000'

In the first case "1" got expanded to "000001" and "100000" was printed as-is. However, when you interpret it as being *after* the decimal point, you would consider the first one to not be zero-padded at all and the second one to be zero-padded on the right.

I think the documentation can just be changed to "zero-padded to 6 digits" without specifying left or right.

[vishalpandeyvip]

I have made a PR into the repository, can anyone please review and merge it.

[iritkatriel]

New changeset f97ec09 by Vishal Pandey in branch 'main':
bpo-33381: [doc] strftime's %f option may pad zeros on the left or the right (GH-29801)
f97ec09