hist as backwards compatible as possible with polars<1.0

narwhals/_polars/series.py

@@ -425,6 +425,13 @@ def hist(
         include_breakpoint: bool = True,
     ) -> PolarsDataFrame:
         from narwhals._polars.dataframe import PolarsDataFrame
+        from narwhals.exceptions import InvalidOperationError
+
+        if bins is not None:
+            for i in range(1, len(bins)):
+                if bins[i - 1] >= bins[i]:
+                    msg = "bins must increase monotonically"
+                    raise InvalidOperationError(msg)
 
         df = self._native_series.hist(
             bins=bins,
@@ -435,6 +442,15 @@ def hist(
         if not include_category and not include_breakpoint:
             df.columns = ["count"]
 
+        if self._backend_version < (1, 0):  # pragma: no cover
+            if (
+                bins is not None
+            ):  #  polars<1.0 implicitly adds -inf and inf to either end of bins
+                r = pl.int_range(0, len(df))
+                df = df.filter((r > 0) & (r < len(df) - 1))
+            if include_breakpoint:
+                df = df.rename({"break_point": "breakpoint"})
+
         return PolarsDataFrame(
             df, backend_version=self._backend_version, version=self._version
         )

tests/series_only/hist_test.py

@@ -8,6 +8,7 @@
 
 import narwhals.stable.v1 as nw
 from narwhals.exceptions import InvalidOperationError
+from tests.utils import POLARS_VERSION
 from tests.utils import ConstructorEager
 from tests.utils import assert_equal_data
 from tests.utils import nwise
@@ -109,6 +110,10 @@ def test_hist_bin(
     assert_equal_data(result, expected)
 
 
+@pytest.mark.skipif(
+    POLARS_VERSION < (1, 0),
+    reason="hist(bin_count=...) behavior significantly changed after 1.0",
+)
 @pytest.mark.parametrize("params", counts_and_expected)
 @pytest.mark.parametrize("include_breakpoint", [True, False])
 @pytest.mark.parametrize("include_category", [True, False])
@@ -229,6 +234,10 @@ def test_hist_bins_hypotheis(
     ),
     bin_count=st.integers(min_value=0, max_value=1_000),
 )
+@pytest.mark.skipif(
+    POLARS_VERSION < (1, 0),
+    reason="hist(bin_count=...) behavior significantly changed after 1.0",
+)
 @pytest.mark.filterwarnings(
     "ignore:`Series.hist` is being called from the stable API although considered an unstable feature."
 )