Fix various .str methods for pandas compatability (rapidsai#17782)

closes rapidsai#17745
closes rapidsai#17748
closes rapidsai#17749
closes rapidsai#17751

Authors:
  - Matthew Roeschke (https://github.com/mroeschke)

Approvers:
  - Vyas Ramasubramani (https://github.com/vyasr)

URL: rapidsai#17782

python/cudf/cudf/core/column/string.py

@@ -1068,6 +1068,10 @@ def replace(
         if regex and isinstance(pat, re.Pattern):
             pat = pat.pattern
 
+        pa_repl = pa.scalar(repl)
+        if not pa.types.is_string(pa_repl.type):
+            raise TypeError(f"repl must be a str, not {type(repl).__name__}.")
+
         # Pandas forces non-regex replace when pat is a single-character
         with acquire_spill_lock():
             if regex is True and len(pat) > 1:
@@ -1076,14 +1080,14 @@ def replace(
                     plc.strings.regex_program.RegexProgram.create(
                         pat, plc.strings.regex_flags.RegexFlags.DEFAULT
                     ),
-                    pa_scalar_to_plc_scalar(pa.scalar(repl)),
+                    pa_scalar_to_plc_scalar(pa_repl),
                     n,
                 )
             else:
                 plc_result = plc.strings.replace.replace(
                     self._column.to_pylibcudf(mode="read"),
                     pa_scalar_to_plc_scalar(pa.scalar(pat)),
-                    pa_scalar_to_plc_scalar(pa.scalar(repl)),
+                    pa_scalar_to_plc_scalar(pa_repl),
                     n,
                 )
             result = Column.from_pylibcudf(plc_result)
@@ -2416,13 +2420,19 @@ def get(self, i: int = 0) -> SeriesOrIndex:
         2    f
         dtype: object
         """
+        str_lens = self.len()
         if i < 0:
             next_index = i - 1
             step = -1
+            to_mask = str_lens < abs(i)  # type: ignore[operator]
         else:
             next_index = i + 1
             step = 1
-        return self.slice(i, next_index, step)
+            to_mask = str_lens <= i  # type: ignore[operator]
+        result = self.slice(i, next_index, step)
+        if to_mask.any():  # type: ignore[union-attr]
+            result[to_mask] = cudf.NA  # type: ignore[index]
+        return result
 
     def get_json_object(
         self,
@@ -3933,27 +3943,26 @@ def isspace(self) -> SeriesOrIndex:
     def _starts_ends_with(
         self,
         method: Callable[[plc.Column, plc.Column | plc.Scalar], plc.Column],
-        pat: str | Sequence,
+        pat: str | tuple[str, ...],
     ) -> SeriesOrIndex:
-        if pat is None:
-            raise TypeError(
-                f"expected a string or a sequence-like object, not "
-                f"{type(pat).__name__}"
-            )
-        elif is_scalar(pat):
+        if isinstance(pat, str):
             plc_pat = pa_scalar_to_plc_scalar(pa.scalar(pat, type=pa.string()))
-        else:
+        elif isinstance(pat, tuple) and all(isinstance(p, str) for p in pat):
             plc_pat = column.as_column(pat, dtype="str").to_pylibcudf(
                 mode="read"
             )
+        else:
+            raise TypeError(
+                f"expected a string or tuple, not {type(pat).__name__}"
+            )
         with acquire_spill_lock():
             plc_result = method(
                 self._column.to_pylibcudf(mode="read"), plc_pat
             )
             result = Column.from_pylibcudf(plc_result)
         return self._return_or_inplace(result)
 
-    def endswith(self, pat: str | Sequence) -> SeriesOrIndex:
+    def endswith(self, pat: str | tuple[str, ...]) -> SeriesOrIndex:
         """
         Test if the end of each string element matches a pattern.
 
@@ -3997,7 +4006,7 @@ def endswith(self, pat: str | Sequence) -> SeriesOrIndex:
         """
         return self._starts_ends_with(plc.strings.find.ends_with, pat)
 
-    def startswith(self, pat: str | Sequence) -> SeriesOrIndex:
+    def startswith(self, pat: str | tuple[str, ...]) -> SeriesOrIndex:
         """
         Test if the start of each string element matches a pattern.
 
@@ -4299,6 +4308,8 @@ def index(
 
         if (result == -1).any():
             raise ValueError("substring not found")
+        elif cudf.get_option("mode.pandas_compatible"):
+            return result.astype(np.dtype(np.int64))
         else:
             return result
 
@@ -4359,6 +4370,8 @@ def rindex(
 
         if (result == -1).any():
             raise ValueError("substring not found")
+        elif cudf.get_option("mode.pandas_compatible"):
+            return result.astype(np.dtype(np.int64))
         else:
             return result
 

python/cudf/cudf/tests/test_string.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2018-2024, NVIDIA CORPORATION.
+# Copyright (c) 2018-2025, NVIDIA CORPORATION.
 
 import json
 import re
@@ -2048,26 +2048,26 @@ def test_string_starts_ends(data, pat):
     [
         (
             ["abc", "xyz", "a", "ab", "123", "097"],
-            ["abc", "x", "a", "b", "3", "7"],
+            ("abc", "x", "a", "b", "3", "7"),
         ),
-        (["A B", "1.5", "3,000"], ["A ", ".", ","]),
-        (["23", "³", "⅕", ""], ["23", "³", "⅕", ""]),
-        ([" ", "\t\r\n ", ""], ["d", "\n ", ""]),
+        (["A B", "1.5", "3,000"], ("A ", ".", ",")),
+        (["23", "³", "⅕", ""], ("23", "³", "⅕", "")),
+        ([" ", "\t\r\n ", ""], ("d", "\n ", "")),
         (
             ["$", "B", "Aab$", "$$ca", "C$B$", "cat"],
-            ["$", "$", "a", "<", "(", "#"],
+            ("$", "$", "a", "<", "(", "#"),
         ),
         (
             ["line to be wrapped", "another line to be wrapped"],
-            ["another", "wrapped"],
+            ("another", "wrapped"),
         ),
         (
             ["hello", "there", "world", "+1234", "-1234", None, "accént", ""],
-            ["hsdjfk", None, "ll", "+", "-", "w", "-", "én"],
+            ("hsdjfk", "", "ll", "+", "-", "w", "-", "én"),
         ),
         (
             ["1. Ant.  ", "2. Bee!\n", "3. Cat?\t", None],
-            ["1. Ant.  ", "2. Bee!\n", "3. Cat?\t", None],
+            ("1. Ant.  ", "2. Bee!\n", "3. Cat?\t", ""),
         ),
     ],
 )
@@ -3539,3 +3539,39 @@ def test_string_reduction_error():
         lfunc_args_and_kwargs=([], {"skipna": False}),
         rfunc_args_and_kwargs=([], {"skipna": False}),
     )
+
+
+def test_getitem_out_of_bounds():
+    data = ["123", "12", "1"]
+    pd_ser = pd.Series(data)
+    cudf_ser = cudf.Series(data)
+    expected = pd_ser.str[2]
+    result = cudf_ser.str[2]
+    assert_eq(result, expected)
+
+    expected = pd_ser.str[-2]
+    result = cudf_ser.str[-2]
+    assert_eq(result, expected)
+
+
+@pytest.mark.parametrize("method", ["startswith", "endswith"])
+@pytest.mark.parametrize("pat", [None, (1, 2), pd.Series([1])])
+def test_startsendwith_invalid_pat(method, pat):
+    ser = cudf.Series(["1"])
+    with pytest.raises(TypeError):
+        getattr(ser.str, method)(pat)
+
+
+@pytest.mark.parametrize("method", ["rindex", "index"])
+def test_index_int64_pandas_compat(method):
+    data = ["ABCDEFG", "BCDEFEF", "DEFGHIJEF", "EFGHEF"]
+    with cudf.option_context("mode.pandas_compatible", True):
+        result = getattr(cudf.Series(data).str, method)("E", 4, 8)
+    expected = getattr(pd.Series(data).str, method)("E", 4, 8)
+    assert_eq(result, expected)
+
+
+def test_replace_invalid_scalar_repl():
+    ser = cudf.Series(["1"])
+    with pytest.raises(TypeError):
+        ser.str.replace("1", 2)