Added test for Expr.str contains method

narwhals/expression.py

@@ -1462,7 +1462,7 @@ def ends_with(self, suffix: str) -> Expr:
             lambda plx: self._expr._call(plx).str.ends_with(suffix)
         )
 
-    def contains(self, pattern: str, literal: bool = False) -> Expr:
+    def contains(self, pattern: str | Expr, literal: bool = False) -> Expr:
         """
         Check if string contains a substring that matches a pattern.
 

narwhals/series.py

@@ -1612,7 +1612,7 @@ def __init__(self, series: Series) -> None:
     def ends_with(self, suffix: str) -> Series:
         return self._series.__class__(self._series._series.str.ends_with(suffix))
 
-    def contains(self, pattern: str, literal: bool = False) -> Series:
+    def contains(self, pattern: str | Expr, literal: bool = False) -> Series:
         return self._series.__class__(
             self._series._series.str.contains(pattern, literal=literal)
         )

tests/expr/str/contains_test.py

@@ -0,0 +1,31 @@
+from typing import Any
+
+import pandas as pd
+import polars as pl
+import pytest
+
+import narwhals as nw
+from tests.utils import compare_dicts
+
+data = {
+    "pets": ["cat", "dog", "rabbit and parrot", "dove"]
+}
+
+df_pandas = pd.DataFrame(data)
+df_polars = pl.DataFrame(data)
+
+@pytest.mark.parametrize("df_any", [df_pandas, df_polars])
+def test_contains(df_any: Any) -> None:
+    df = nw.from_native(df_any, eager_only=True)
+    result = df.with_columns(
+        case_insensitive_match=nw.col("pets").str.contains("(?i)parrot|Dove")
+    )
+    expected = {
+        "pets": ["cat", "dog", "rabbit and parrot", "dove"],
+        "case_insensitive_match": [False, False, True, True]
+    }
+    compare_dicts(result, expected)
+    result = df.with_columns(
+        case_insensitive_match=df["pets"].str.contains("(?i)parrot|Dove")
+    )
+    compare_dicts(result, expected)