Add date attribute to datetime accessor (#4994)

* add date accessor to accessor_dt.py (GH4983)

* raise error when using date with CFTimeIndex

* Add tests

* Mention changes in whats-new.rst

* Add DatetimeAccessor.date to api-hidden.rst

* Add attribute to api.rst

* Change AttributeError message

Author: observingClouds

doc/api-hidden.rst

@@ -287,6 +287,7 @@
    core.accessor_dt.DatetimeAccessor.floor
    core.accessor_dt.DatetimeAccessor.round
    core.accessor_dt.DatetimeAccessor.strftime
+   core.accessor_dt.DatetimeAccessor.date
    core.accessor_dt.DatetimeAccessor.day
    core.accessor_dt.DatetimeAccessor.dayofweek
    core.accessor_dt.DatetimeAccessor.dayofyear

doc/api.rst

@@ -507,6 +507,7 @@ Datetimelike properties
    DataArray.dt.daysinmonth
    DataArray.dt.season
    DataArray.dt.time
+   DataArray.dt.date
    DataArray.dt.is_month_start
    DataArray.dt.is_month_end
    DataArray.dt.is_quarter_end

doc/whats-new.rst

@@ -51,12 +51,13 @@ New Features
   grant from the `Chan Zuckerberg Initiative <https://chanzuckerberg.com>`_ and
   developed by `B-Open <https://www.bopen.eu>`_.
   By `Aureliana Barghini <https://github.com/aurghs>`_ and `Alessandro Amici <https://github.com/alexamici>`_.
+- :py:attr:`~core.accessor_dt.DatetimeAccessor.date` added (:issue:`4983`, :pull:`4994`).
+  By `Hauke Schulz <https://github.com/observingClouds>`_.
 - Implement ``__getitem__`` for both :py:class:`~core.groupby.DatasetGroupBy` and
   :py:class:`~core.groupby.DataArrayGroupBy`, inspired by pandas'
   :py:meth:`~pandas.core.groupby.GroupBy.get_group`.
   By `Deepak Cherian <https://github.com/dcherian>`_.
 
-
 Breaking changes
 ~~~~~~~~~~~~~~~~
 - :py:func:`open_dataset` and :py:func:`open_dataarray` now accept only the first argument

xarray/core/accessor_dt.py

@@ -31,6 +31,10 @@ def _access_through_cftimeindex(values, name):
     if name == "season":
         months = values_as_cftimeindex.month
         field_values = _season_from_months(months)
+    elif name == "date":
+        raise AttributeError(
+            "'CFTimeIndex' object has no attribute `date`. Consider using the floor method instead, for instance: `.time.dt.floor('D')`."
+        )
     else:
         field_values = getattr(values_as_cftimeindex, name)
     return field_values.reshape(values.shape)
@@ -415,6 +419,10 @@ def weekofyear(self):
         "time", "Timestamps corresponding to datetimes", object
     )
 
+    date = Properties._tslib_field_accessor(
+        "date", "Date corresponding to datetimes", object
+    )
+
     is_month_start = Properties._tslib_field_accessor(
         "is_month_start",
         "Indicates whether the date is the first day of the month.",

xarray/tests/test_accessor_dt.py

@@ -59,6 +59,8 @@ def setup(self):
             "weekday",
             "dayofyear",
             "quarter",
+            "date",
+            "time",
             "is_month_start",
             "is_month_end",
             "is_quarter_start",
@@ -144,6 +146,8 @@ def test_not_datetime_type(self):
             "weekday",
             "dayofyear",
             "quarter",
+            "date",
+            "time",
             "is_month_start",
             "is_month_end",
             "is_quarter_start",
@@ -430,6 +434,16 @@ def test_isocalendar_cftime(data):
         data.time.dt.isocalendar()
 
 
+@requires_cftime
+def test_date_cftime(data):
+
+    with raises_regex(
+        AttributeError,
+        r"'CFTimeIndex' object has no attribute `date`. Consider using the floor method instead, for instance: `.time.dt.floor\('D'\)`.",
+    ):
+        data.time.dt.date()
+
+
 @requires_cftime
 @pytest.mark.filterwarnings("ignore::RuntimeWarning")
 def test_cftime_strftime_access(data):