date_range: set default freq to 'D' only if periods, start, or end are None (#8774)

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

* Addressed feedback: Updated default argument handling in cftime_range to ensure consistency across date range functions

* Update doc/whats-new.rst

Co-authored-by: Mathias Hauser <mathause@users.noreply.github.com>

* Update xarray/tests/test_cftime_offsets.py

Co-authored-by: Mathias Hauser <mathause@users.noreply.github.com>

* Update xarray/tests/test_cftime_offsets.py

Co-authored-by: Mathias Hauser <mathause@users.noreply.github.com>

* Input argument period included in test_cftime_range_no_freq and test_date_range_no_freq following #8770

* Update doc/whats-new.rst

Co-authored-by: Spencer Clark <spencerkclark@gmail.com>

---------

Co-authored-by: Mathias Hauser <mathause@users.noreply.github.com>
Co-authored-by: Spencer Clark <spencerkclark@gmail.com>

Author: 3 people

doc/whats-new.rst

@@ -37,7 +37,9 @@ Deprecations
 
 Bug fixes
 ~~~~~~~~~
-
+- The default ``freq`` parameter in :py:meth:`xr.date_range` and :py:meth:`xr.cftime_range` is
+  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

@@ -1294,7 +1294,6 @@ def test_cftime_range_name():
         (None, None, 5, "YE", None),
         ("2000", None, None, "YE", None),
         (None, "2000", None, "YE", None),
-        ("2000", "2001", None, None, None),
         (None, None, None, None, None),
         ("2000", "2001", None, "YE", "up"),
         ("2000", "2001", 5, "YE", None),
@@ -1733,3 +1732,47 @@ def test_cftime_range_same_as_pandas(start, end, freq):
     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, periods",
+    [
+        ("2022-01-01", "2022-01-10", 2),
+        ("2022-03-01", "2022-03-31", 2),
+        ("2022-01-01", "2022-01-10", None),
+        ("2022-03-01", "2022-03-31", None),
+    ],
+)
+def test_cftime_range_no_freq(start, end, periods):
+    """
+    Test whether cftime_range produces the same result as Pandas
+    when freq is not provided, but start, end and periods are.
+    """
+    # Generate date ranges using cftime_range
+    result = cftime_range(start=start, end=end, periods=periods)
+    result = result.to_datetimeindex()
+    expected = pd.date_range(start=start, end=end, periods=periods)
+
+    np.testing.assert_array_equal(result, expected)
+
+
+@pytest.mark.parametrize(
+    "start, end, periods",
+    [
+        ("2022-01-01", "2022-01-10", 2),
+        ("2022-03-01", "2022-03-31", 2),
+        ("2022-01-01", "2022-01-10", None),
+        ("2022-03-01", "2022-03-31", None),
+    ],
+)
+def test_date_range_no_freq(start, end, periods):
+    """
+    Test whether date_range produces the same result as Pandas
+    when freq is not provided, but start, end and periods are.
+    """
+    # Generate date ranges using date_range
+    result = date_range(start=start, end=end, periods=periods)
+    expected = pd.date_range(start=start, end=end, periods=periods)
+
+    np.testing.assert_array_equal(result, expected)