Bug pyarrow implementation of str.fullmatch matches partial string. issue #56652 (#56691)

* BUG-Pyarrow-implementation-of-str.fullmatch-matches-partial-string.-Issue-#56652

changed array.py: Makes Series(["abc$abc]).str.fullmatch("abc\\$") give the same result as when dtype = pyarow.string as opposed to dtype = str.

Issue reporter (Issue-#56652) requested change "//$" to "\$", but this resulted in DepreciationWarnng, so used "\\$" instead.

Change test_arrow.py: updated test_str_fullmatch to account for edge cases where string starts with and ends with literal $ as well as ends with the string.

* tidy

* Update and test string_arrow._str_fullmatch

Changed: string_arrow: because it shoud be conistent with other changes. Affects circumstance where dtype="string[pyarrow]" as opposed to dtype=pd.ArrowDtype(pa.string())

Changed: test_find_replace.py: Added unit test for the edge cases where the user wants o search for a string that ends in a literal dollar sign. The string_arrow.oy updates effect this also.

Question: For consistency, I formatted test_fullmatch_dollar_literal() to match other unit tests in .py - Should I instead aim to implement @pytest.mark.parametrize, which is in consistent, but more in line with developer guidelines?

* Update v2.2.0.rst

Author: JackCollins91

doc/source/whatsnew/v2.2.0.rst

@@ -805,6 +805,7 @@ Strings
 - Bug in :meth:`Series.str.replace` when ``n < 0`` for :class:`ArrowDtype` with ``pyarrow.string`` (:issue:`56404`)
 - Bug in :meth:`Series.str.startswith` and :meth:`Series.str.endswith` with arguments of type ``tuple[str, ...]`` for :class:`ArrowDtype` with ``pyarrow.string`` dtype (:issue:`56579`)
 - Bug in :meth:`Series.str.startswith` and :meth:`Series.str.endswith` with arguments of type ``tuple[str, ...]`` for ``string[pyarrow]`` (:issue:`54942`)
+- Bug in :meth:`str.fullmatch` when ``dtype=pandas.ArrowDtype(pyarrow.string()))`` allows partial matches when regex ends in literal //$ (:issue:`56652`)
 - Bug in comparison operations for ``dtype="string[pyarrow_numpy]"`` raising if dtypes can't be compared (:issue:`56008`)
 
 Interval

pandas/core/arrays/arrow/array.py

@@ -2296,7 +2296,7 @@ def _str_match(
     def _str_fullmatch(
         self, pat, case: bool = True, flags: int = 0, na: Scalar | None = None
     ) -> Self:
-        if not pat.endswith("$") or pat.endswith("//$"):
+        if not pat.endswith("$") or pat.endswith("\\$"):
             pat = f"{pat}$"
         return self._str_match(pat, case, flags, na)
 

pandas/core/arrays/string_arrow.py

@@ -436,7 +436,7 @@ def _str_match(
     def _str_fullmatch(
         self, pat, case: bool = True, flags: int = 0, na: Scalar | None = None
     ):
-        if not pat.endswith("$") or pat.endswith("//$"):
+        if not pat.endswith("$") or pat.endswith("\\$"):
             pat = f"{pat}$"
         return self._str_match(pat, case, flags, na)
 

pandas/tests/extension/test_arrow.py

@@ -1898,16 +1898,21 @@ def test_str_match(pat, case, na, exp):
 @pytest.mark.parametrize(
     "pat, case, na, exp",
     [
-        ["abc", False, None, [True, None]],
-        ["Abc", True, None, [False, None]],
-        ["bc", True, None, [False, None]],
-        ["ab", False, True, [True, True]],
-        ["a[a-z]{2}", False, None, [True, None]],
-        ["A[a-z]{1}", True, None, [False, None]],
+        ["abc", False, None, [True, True, False, None]],
+        ["Abc", True, None, [False, False, False, None]],
+        ["bc", True, None, [False, False, False, None]],
+        ["ab", False, None, [True, True, False, None]],
+        ["a[a-z]{2}", False, None, [True, True, False, None]],
+        ["A[a-z]{1}", True, None, [False, False, False, None]],
+        # GH Issue: #56652
+        ["abc$", False, None, [True, False, False, None]],
+        ["abc\\$", False, None, [False, True, False, None]],
+        ["Abc$", True, None, [False, False, False, None]],
+        ["Abc\\$", True, None, [False, False, False, None]],
     ],
 )
 def test_str_fullmatch(pat, case, na, exp):
-    ser = pd.Series(["abc", None], dtype=ArrowDtype(pa.string()))
+    ser = pd.Series(["abc", "abc$", "$abc", None], dtype=ArrowDtype(pa.string()))
     result = ser.str.match(pat, case=case, na=na)
     expected = pd.Series(exp, dtype=ArrowDtype(pa.bool_()))
     tm.assert_series_equal(result, expected)

pandas/tests/strings/test_find_replace.py

@@ -730,6 +730,15 @@ def test_fullmatch(any_string_dtype):
     tm.assert_series_equal(result, expected)
 
 
+def test_fullmatch_dollar_literal(any_string_dtype):
+    # GH 56652
+    ser = Series(["foo", "foo$foo", np.nan, "foo$"], dtype=any_string_dtype)
+    result = ser.str.fullmatch("foo\\$")
+    expected_dtype = "object" if any_string_dtype in object_pyarrow_numpy else "boolean"
+    expected = Series([False, False, np.nan, True], dtype=expected_dtype)
+    tm.assert_series_equal(result, expected)
+
+
 def test_fullmatch_na_kwarg(any_string_dtype):
     ser = Series(
         ["fooBAD__barBAD", "BAD_BADleroybrown", np.nan, "foo"], dtype=any_string_dtype