BUG: fix fillna on series with integers, close #1788

Author: lodagro

pandas/core/series.py

@@ -16,7 +16,7 @@
 
 from pandas.core.common import (isnull, notnull, _is_bool_indexer,
                                 _default_index, _maybe_upcast,
-                                _asarray_tuplesafe)
+                                _asarray_tuplesafe, is_integer_dtype)
 from pandas.core.index import (Index, MultiIndex, InvalidIndexError,
                                _ensure_index, _handle_legacy_indexes)
 from pandas.core.indexing import _SeriesIndexer
@@ -386,6 +386,10 @@ def __init__(self, data=None, index=None, dtype=None, name=None,
     def _constructor(self):
         return Series
 
+    @property
+    def _can_hold_na(self):
+        return not is_integer_dtype(self.dtype)
+
     def __hash__(self):
         raise TypeError('unhashable type')
 
@@ -2157,6 +2161,9 @@ def fillna(self, value=None, method='pad', inplace=False,
         -------
         filled : Series
         """
+        if not self._can_hold_na:
+            return self.copy() if not inplace else self
+
         if value is not None:
             result = self.copy() if not inplace else self
             mask = isnull(self.values)

pandas/tests/test_series.py

@@ -2697,6 +2697,11 @@ def test_isin(self):
         expected = Series([True, False, True, False, False, False, True, True])
         assert_series_equal(result, expected)
 
+    def test_fillna_int(self):
+        s = Series(np.random.randint(-100, 100, 50))
+        self.assert_(s.fillna(inplace=True) is s)
+        assert_series_equal(s.fillna(inplace=False), s)
+
 #-------------------------------------------------------------------------------
 # TimeSeries-specific