Fixing issue #8770: Improved frequency parameter logic to set it to 'D' only if periods, start, or end are None.

doc/whats-new.rst

@@ -34,7 +34,9 @@ Deprecations
 
 Bug fixes
 ~~~~~~~~~
-
+- The logic of the frequency parameter in :py:meth:`xr.date_range` and :py:meth:`xr.cftime_range` are
+  set to 'D' only if periods, start, or end are None. (:issue:`8770`, :pull:`8774`).
+  By `Roberto Chang <https://github.com/rjavierch>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/coding/cftime_offsets.py

@@ -914,7 +914,7 @@ def cftime_range(
     start=None,
     end=None,
     periods=None,
-    freq="D",
+    freq=None,
     normalize=False,
     name=None,
     closed: NoDefault | SideOptions = no_default,
@@ -1100,6 +1100,10 @@ def cftime_range(
     --------
     pandas.date_range
     """
+
+    if freq is None and any(arg is None for arg in [periods, start, end]):
+        freq = "D"
+
     # Adapted from pandas.core.indexes.datetimes._generate_range.
     if count_not_none(start, end, periods, freq) != 3:
         raise ValueError(
@@ -1152,7 +1156,7 @@ def date_range(
     start=None,
     end=None,
     periods=None,
-    freq="D",
+    freq=None,
     tz=None,
     normalize=False,
     name=None,

xarray/tests/test_cftime_offsets.py

@@ -1307,8 +1307,8 @@
     freq: str | None,
     inclusive: Literal["up", None],
 ) -> None:
     with pytest.raises(ValueError):
         cftime_range(start, end, periods, freq, inclusive=inclusive)  # type: ignore[arg-type]
 
 
 def test_invalid_cftime_arg() -> None:
@@ -1733,3 +1733,47 @@
     expected = date_range(start, end, freq=freq, use_cftime=False)
 
     np.testing.assert_array_equal(result, expected)
+
+
+@pytest.mark.filterwarnings("ignore:Converting a CFTimeIndex with:")
+@pytest.mark.parametrize(
+    "start, end",
+    [
+        ("2022-01-01", "2022-01-10"),
+        ("2022-02-01", "2022-02-28"),
+        ("2022-03-01", "2022-03-31"),
+    ],
+)
+def test_cftime_range_no_freq(start, end):
+    """
+    Test whether cftime_range produces the same result as Pandas
+    when freq is not provided, but start and end are.
+    """
+    # Generate date ranges using cftime_range
+    result = cftime_range(start=start, end=end)
+    result = result.to_datetimeindex()
+    expected = pd.date_range(start=start, end=end)
+
+    # Assert that the results are equal
+    np.testing.assert_array_equal(result, expected)
+
+
+@pytest.mark.parametrize(
+    "start, end",
+    [
+        ("2022-01-01", "2022-01-10"),
+        ("2022-02-01", "2022-02-28"),
+        ("2022-03-01", "2022-03-31"),
+    ],
+)
+def test_date_range_no_freq(start, end):
+    """
+    Test whether date_range produces the same result as Pandas
+    when freq is not provided, but start and end are.
+    """
+    # Generate date ranges using date_range
+    result = date_range(start=start, end=end)
+    expected = pd.date_range(start=start, end=end)
+
+    # Assert that the results are equal
+    np.testing.assert_array_equal(result, expected)