From 97c8c18174a8354ced1d22b98d7a8c141c3f9c9d Mon Sep 17 00:00:00 2001
From: Maximilian Roos <5635139+max-sixty@users.noreply.github.com>
Date: Thu, 8 Feb 2024 18:21:46 -0800
Subject: [PATCH] Switch `.dt` to raise an `AttributeError` (#8724)

* Switch `.dt` to raise an `AttributeError`

Discussion at #8718

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---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
---
 doc/whats-new.rst                | 3 +++
 xarray/core/accessor_dt.py       | 6 +++++-
 xarray/tests/test_accessor_dt.py | 4 ++--
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index dc4fb7ae722..b2c4a0b5257 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -82,6 +82,9 @@ Documentation
 Internal Changes
 ~~~~~~~~~~~~~~~~
 
+- ``DataArray.dt`` now raises an ``AttributeError`` rather than a ``TypeError``
+  when the data isn't datetime-like. (:issue:`8718`, :pull:`8724`)
+  By `Maximilian Roos <https://github.com/max-sixty>`_.
 
 .. _whats-new.2024.01.1:
 
diff --git a/xarray/core/accessor_dt.py b/xarray/core/accessor_dt.py
index 0745a72af2f..219bca90048 100644
--- a/xarray/core/accessor_dt.py
+++ b/xarray/core/accessor_dt.py
@@ -616,7 +616,11 @@ def __new__(cls, obj: T_DataArray) -> CombinedDatetimelikeAccessor:
         # appropriate. Since we're checking the dtypes anyway, we'll just
         # do all the validation here.
         if not _contains_datetime_like_objects(obj.variable):
-            raise TypeError(
+            # We use an AttributeError here so that `obj.dt` raises an error that
+            # `getattr` expects; https://github.com/pydata/xarray/issues/8718. It's a
+            # bit unusual in a `__new__`, but that's the only case where we use this
+            # class.
+            raise AttributeError(
                 "'.dt' accessor only available for "
                 "DataArray with datetime64 timedelta64 dtype or "
                 "for arrays containing cftime datetime "
diff --git a/xarray/tests/test_accessor_dt.py b/xarray/tests/test_accessor_dt.py
index 387929d3fe9..d751d91df5e 100644
--- a/xarray/tests/test_accessor_dt.py
+++ b/xarray/tests/test_accessor_dt.py
@@ -145,7 +145,7 @@ def test_not_datetime_type(self) -> None:
         nontime_data = self.data.copy()
         int_data = np.arange(len(self.data.time)).astype("int8")
         nontime_data = nontime_data.assign_coords(time=int_data)
-        with pytest.raises(TypeError, match=r"dt"):
+        with pytest.raises(AttributeError, match=r"dt"):
             nontime_data.time.dt
 
     @pytest.mark.filterwarnings("ignore:dt.weekofyear and dt.week have been deprecated")
@@ -310,7 +310,7 @@ def test_not_datetime_type(self) -> None:
         nontime_data = self.data.copy()
         int_data = np.arange(len(self.data.time)).astype("int8")
         nontime_data = nontime_data.assign_coords(time=int_data)
-        with pytest.raises(TypeError, match=r"dt"):
+        with pytest.raises(AttributeError, match=r"dt"):
             nontime_data.time.dt
 
     @pytest.mark.parametrize(