BUG: maximum recursion error when replacing empty lists (#22083)

doc/source/whatsnew/v0.24.0.txt

@@ -667,6 +667,7 @@ Reshaping
 - Bug in :meth:`DataFrame.replace` raises RecursionError when converting OutOfBounds ``datetime64[ns, tz]`` (:issue:`20380`)
 - :func:`pandas.core.groupby.GroupBy.rank` now raises a ``ValueError`` when an invalid value is passed for argument ``na_option`` (:issue:`22124`)
 - Bug in :func:`get_dummies` with Unicode attributes in Python 2 (:issue:`22084`)
+- Bug in :meth:`DataFrame.replace` raises ``RecursionError`` when replacing empty lists (:issue:`22083`)
 -
 
 Build Changes

pandas/core/internals/blocks.py

@@ -777,10 +777,9 @@ def copy(self, deep=True, mgr=None):
 
     def replace(self, to_replace, value, inplace=False, filter=None,
                 regex=False, convert=True, mgr=None):
-        """ replace the to_replace value with value, possible to create new
+        """replace the to_replace value with value, possible to create new
         blocks here this is just a call to putmask. regex is not used here.
-        It is used in ObjectBlocks.  It is here for API
-        compatibility.
+        It is used in ObjectBlocks.  It is here for API compatibility.
         """
 
         inplace = validate_bool_kwarg(inplace, 'inplace')
@@ -802,6 +801,11 @@ def replace(self, to_replace, value, inplace=False, filter=None,
                                     copy=not inplace) for b in blocks]
             return blocks
         except (TypeError, ValueError):
+            # GH 22083, TypeError or ValueError occurred within error handling
+            # causes infinite loop. Cast and retry only if not objectblock.
+            if is_object_dtype(self):
+                raise
+
             # try again with a compatible block
             block = self.astype(object)
             return block.replace(to_replace=original_to_replace,

pandas/core/missing.py

@@ -68,6 +68,10 @@ def mask_missing(arr, values_to_mask):
         else:
             mask |= isna(arr)
 
+    # GH 21977
+    if mask is None:
+        mask = np.zeros(arr.shape, dtype=bool)
+
     return mask
 
 

pandas/tests/frame/test_replace.py

@@ -603,6 +603,20 @@ def test_replace_list(self):
 
         assert_frame_equal(res, expec)
 
+    def test_replace_with_empty_list(self):
+        # GH 21977
+        s = pd.Series([['a', 'b'], [], np.nan, [1]])
+        df = pd.DataFrame({'col': s})
+        expected = df
+        result = df.replace([], np.nan)
+        assert_frame_equal(result, expected)
+
+        # GH 19266
+        with tm.assert_raises_regex(ValueError, "cannot assign mismatch"):
+            df.replace({np.nan: []})
+        with tm.assert_raises_regex(ValueError, "cannot assign mismatch"):
+            df.replace({np.nan: ['dummy', 'alt']})
+
     def test_replace_series_dict(self):
         # from GH 3064
         df = DataFrame({'zero': {'a': 0.0, 'b': 1}, 'one': {'a': 2.0, 'b': 0}})

pandas/tests/series/test_replace.py

@@ -130,6 +130,19 @@ def test_replace_with_single_list(self):
             s.replace([1, 2, 3], inplace=True, method='crash_cymbal')
         tm.assert_series_equal(s, ser)
 
+    def test_replace_with_empty_list(self):
+        # GH 21977
+        s = pd.Series([[1], [2, 3], [], np.nan, [4]])
+        expected = s
+        result = s.replace([], np.nan)
+        tm.assert_series_equal(result, expected)
+
+        # GH 19266
+        with tm.assert_raises_regex(ValueError, "cannot assign mismatch"):
+            s.replace({np.nan: []})
+        with tm.assert_raises_regex(ValueError, "cannot assign mismatch"):
+            s.replace({np.nan: ['dummy', 'alt']})
+
     def test_replace_mixed_types(self):
         s = pd.Series(np.arange(5), dtype='int64')