DEPR: fractional periods in date_range, timedelta_range, period_range… (#56036)

* DEPR: fractional periods in date_range, timedelta_range, period_range, interval_range

* GH ref

* DEPR: non-integer periods

Author: jbrockmendel

doc/source/whatsnew/v2.2.0.rst

@@ -272,6 +272,7 @@ Other Deprecations
 - Deprecated :meth:`Index.format`, use ``index.astype(str)`` or ``index.map(formatter)`` instead (:issue:`55413`)
 - Deprecated ``core.internals`` members ``Block``, ``ExtensionBlock``, and ``DatetimeTZBlock``, use public APIs instead (:issue:`55139`)
 - Deprecated ``year``, ``month``, ``quarter``, ``day``, ``hour``, ``minute``, and ``second`` keywords in the :class:`PeriodIndex` constructor, use :meth:`PeriodIndex.from_fields` instead (:issue:`55960`)
+- Deprecated allowing non-integer ``periods`` argument in :func:`date_range`, :func:`timedelta_range`, :func:`period_range`, and :func:`interval_range` (:issue:`56036`)
 - Deprecated allowing non-keyword arguments in :meth:`DataFrame.to_clipboard`. (:issue:`54229`)
 - Deprecated allowing non-keyword arguments in :meth:`DataFrame.to_csv` except ``path_or_buf``. (:issue:`54229`)
 - Deprecated allowing non-keyword arguments in :meth:`DataFrame.to_dict`. (:issue:`54229`)

pandas/core/arrays/datetimelike.py

@@ -2454,6 +2454,14 @@ def validate_periods(periods: int | float | None) -> int | None:
     """
     if periods is not None:
         if lib.is_float(periods):
+            warnings.warn(
+                # GH#56036
+                "Non-integer 'periods' in pd.date_range, pd.timedelta_range, "
+                "pd.period_range, and pd.interval_range are deprecated and "
+                "will raise in a future version.",
+                FutureWarning,
+                stacklevel=find_stack_level(),
+            )
             periods = int(periods)
         elif not lib.is_integer(periods):
             raise TypeError(f"periods must be a number, got {periods}")

pandas/core/indexes/interval.py

@@ -43,7 +43,6 @@
 )
 from pandas.core.dtypes.common import (
     ensure_platform_int,
-    is_float,
     is_float_dtype,
     is_integer,
     is_integer_dtype,
@@ -60,6 +59,7 @@
 from pandas.core.dtypes.missing import is_valid_na_for_dtype
 
 from pandas.core.algorithms import unique
+from pandas.core.arrays.datetimelike import validate_periods
 from pandas.core.arrays.interval import (
     IntervalArray,
     _interval_shared_docs,
@@ -1076,10 +1076,7 @@ def interval_range(
     if not _is_valid_endpoint(end):
         raise ValueError(f"end must be numeric or datetime-like, got {end}")
 
-    if is_float(periods):
-        periods = int(periods)
-    elif not is_integer(periods) and periods is not None:
-        raise TypeError(f"periods must be a number, got {periods}")
+    periods = validate_periods(periods)
 
     if freq is not None and not is_number(freq):
         try:

pandas/tests/indexes/datetimes/test_date_range.py

@@ -139,9 +139,10 @@ def test_date_range_invalid_periods(self):
         with pytest.raises(TypeError, match=msg):
             date_range(start="1/1/2000", periods="foo", freq="D")
 
-    def test_date_range_float_periods(self):
-        # TODO: reconsider allowing this?
-        rng = date_range("1/1/2000", periods=10.5)
+    def test_date_range_fractional_period(self):
+        msg = "Non-integer 'periods' in pd.date_range, pd.timedelta_range"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            rng = date_range("1/1/2000", periods=10.5)
         exp = date_range("1/1/2000", periods=10)
         tm.assert_index_equal(rng, exp)
 

pandas/tests/indexes/interval/test_interval_range.py

@@ -219,12 +219,15 @@ def test_float_subtype(self, start, end, freq):
         expected = "int64" if is_integer(start + end) else "float64"
         assert result == expected
 
-    def test_constructor_coverage(self):
+    def test_interval_range_fractional_period(self):
         # float value for periods
         expected = interval_range(start=0, periods=10)
-        result = interval_range(start=0, periods=10.5)
+        msg = "Non-integer 'periods' in pd.date_range, .* pd.interval_range"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            result = interval_range(start=0, periods=10.5)
         tm.assert_index_equal(result, expected)
 
+    def test_constructor_coverage(self):
         # equivalent timestamp-like start/end
         start, end = Timestamp("2017-01-01"), Timestamp("2017-01-15")
         expected = interval_range(start=start, end=end)

pandas/tests/indexes/period/test_constructors.py

@@ -176,8 +176,10 @@ def test_constructor_invalid_quarters(self):
                     year=range(2000, 2004), quarter=list(range(4)), freq="Q-DEC"
                 )
 
-    def test_constructor_corner(self):
-        result = period_range("2007-01", periods=10.5, freq="M")
+    def test_period_range_fractional_period(self):
+        msg = "Non-integer 'periods' in pd.date_range, pd.timedelta_range"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            result = period_range("2007-01", periods=10.5, freq="M")
         exp = period_range("2007-01", periods=10, freq="M")
         tm.assert_index_equal(result, exp)
 

pandas/tests/indexes/timedeltas/test_constructors.py

@@ -174,11 +174,14 @@ def test_constructor_iso(self):
         result = to_timedelta(durations)
         tm.assert_index_equal(result, expected)
 
-    def test_constructor_coverage(self):
-        rng = timedelta_range("1 days", periods=10.5)
+    def test_timedelta_range_fractional_period(self):
+        msg = "Non-integer 'periods' in pd.date_range, pd.timedelta_range"
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            rng = timedelta_range("1 days", periods=10.5)
         exp = timedelta_range("1 days", periods=10)
         tm.assert_index_equal(rng, exp)
 
+    def test_constructor_coverage(self):
         msg = "periods must be a number, got foo"
         with pytest.raises(TypeError, match=msg):
             timedelta_range(start="1 days", periods="foo", freq="D")