REGR: to_datetime with non-ISO format, float, and nan fails on main

[MarcoGorelli]

• closes REGR: to_datetime with non-ISO format, float, and nan fails on main #50237 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

[MarcoGorelli]

matches

pandas/pandas/_libs/tslib.pyx

Lines 343 to 346 in 6598797

	elif is_integer_object(val) or is_float_object(val):
	if val != val or val == NPY_NAT:
	iresult[i] = NPY_NAT

[mroeschke]

If np.nan was pd.datetime64('NaT') would this hit the elif block added in this PR (and if so could you add a test for it)?

[MarcoGorelli]

hey - no, that would hit this branch:

pandas/pandas/_libs/tslibs/strptime.pyx

Lines 163 to 165 in e8e77c7

	elif checknull_with_nat_and_na(val):
	iresult[i] = NPY_NAT
	continue

, which is covered by a bunch of tests, e.g.

pandas/pandas/tests/tools/test_to_datetime.py

Lines 168 to 189 in e8e77c7

	@pytest.mark.parametrize(
	"input_s",
	[
	# Null values with Strings
	["19801222", "20010112", None],
	["19801222", "20010112", np.nan],
	["19801222", "20010112", NaT],
	["19801222", "20010112", "NaT"],
	# Null values with Integers
	[19801222, 20010112, None],
	[19801222, 20010112, np.nan],
	[19801222, 20010112, NaT],
	[19801222, 20010112, "NaT"],
	],
	)
	def test_to_datetime_format_YYYYMMDD_with_none(self, input_s):
	# GH 30011
	# format='%Y%m%d'
	# with None
	expected = Series([Timestamp("19801222"), Timestamp("20010112"), NaT])
	result = Series(to_datetime(input_s, format="%Y%m%d"))
	tm.assert_series_equal(result, expected)

[mroeschke]

LGTM

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 1.5.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 a5cbd1e52e9078637c899167f40a29b4bc8901b9

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #50238:  REGR: to_datetime with non-ISO format, float, and nan fails on main'

4. Push to a named branch:

git push YOURFORK 1.5.x:auto-backport-of-pr-50238-on-1.5.x

5. Create a PR against branch 1.5.x, I would have named this PR:

"Backport PR #50238 on branch 1.5.x ( REGR: to_datetime with non-ISO format, float, and nan fails on main)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.