BUG: Index.str.partition not nan-safe (#23558)

doc/source/whatsnew/v0.24.0.txt

@@ -1192,7 +1192,7 @@ Numeric
 Strings
 ^^^^^^^
 
--
+- BUG Index.str.partition not nan-safe (:issue:`23558`)
 -
 -
 

pandas/_libs/lib.pyx

@@ -2274,7 +2274,7 @@ def to_object_array_tuples(rows: list):
 
     k = 0
     for i in range(n):
-        tmp = len(rows[i])
+        tmp = 1 if util.is_nan(rows[i]) else len(rows[i])
         if tmp > k:
             k = tmp
 
@@ -2288,7 +2288,7 @@ def to_object_array_tuples(rows: list):
     except Exception:
         # upcast any subclasses to tuple
         for i in range(n):
-            row = tuple(rows[i])
+            row = (rows[i],) if util.is_nan(rows[i]) else tuple(rows[i])
             for j in range(len(row)):
                 result[i, j] = row[j]
 

pandas/tests/test_strings.py

@@ -2493,7 +2493,7 @@ def test_partition_series(self):
                       ('f g', ' ', 'h')])
         tm.assert_series_equal(result, exp)
 
-        # Not splited
+        # Not split
         values = Series(['abc', 'cde', NA, 'fgh'])
         result = values.str.partition('_', expand=False)
         exp = Series([('abc', '', ''), ('cde', '', ''), NA, ('fgh', '', '')])
@@ -2524,28 +2524,30 @@ def test_partition_series(self):
         assert result == [v.rpartition('_') for v in values]
 
     def test_partition_index(self):
-        values = Index(['a_b_c', 'c_d_e', 'f_g_h'])
+        values = Index(['a_b_c', 'c_d_e', 'f_g_h', np.nan])
 
         result = values.str.partition('_', expand=False)
-        exp = Index(np.array([('a', '_', 'b_c'), ('c', '_', 'd_e'), ('f', '_',
-                                                                     'g_h')]))
+        exp = Index(np.array([('a', '_', 'b_c'), ('c', '_', 'd_e'),
+                              ('f', '_', 'g_h'), np.nan]))
         tm.assert_index_equal(result, exp)
         assert result.nlevels == 1
 
         result = values.str.rpartition('_', expand=False)
-        exp = Index(np.array([('a_b', '_', 'c'), ('c_d', '_', 'e'), (
-            'f_g', '_', 'h')]))
+        exp = Index(np.array([('a_b', '_', 'c'), ('c_d', '_', 'e'),
+                              ('f_g', '_', 'h'), np.nan]))
         tm.assert_index_equal(result, exp)
         assert result.nlevels == 1
 
         result = values.str.partition('_')
-        exp = Index([('a', '_', 'b_c'), ('c', '_', 'd_e'), ('f', '_', 'g_h')])
+        exp = Index([('a', '_', 'b_c'), ('c', '_', 'd_e'),
+                     ('f', '_', 'g_h'), (np.nan, np.nan, np.nan)])
         tm.assert_index_equal(result, exp)
         assert isinstance(result, MultiIndex)
         assert result.nlevels == 3
 
         result = values.str.rpartition('_')
-        exp = Index([('a_b', '_', 'c'), ('c_d', '_', 'e'), ('f_g', '_', 'h')])
+        exp = Index([('a_b', '_', 'c'), ('c_d', '_', 'e'),
+                     ('f_g', '_', 'h'), (np.nan, np.nan, np.nan)])
         tm.assert_index_equal(result, exp)
         assert isinstance(result, MultiIndex)
         assert result.nlevels == 3