Bug: Raise ValueError with interpolate limit = 0

add whatsnew

Add similar log to fillna

Update whatsnew with issue and fillna change

Add test for a negative limit

Author: mroeschke

doc/source/whatsnew/v0.20.0.txt

@@ -241,6 +241,7 @@ Other API Changes
 - ``CParserError`` has been renamed to ``ParserError`` in ``pd.read_csv`` and will be removed in the future (:issue:`12665`)
 - ``SparseArray.cumsum()`` and ``SparseSeries.cumsum()`` will now always return ``SparseArray`` and ``SparseSeries`` respectively (:issue:`12855`)
 - ``DataFrame.applymap()`` with an empty ``DataFrame`` will return a copy of the empty ``DataFrame`` instead of a ``Series`` (:issue:`8222`)
+- ``interpolate()`` and ``fillna()`` will raise a ``ValueError`` if the ``limit`` keyword argument is not greater than 0. (:issue:`9217`)
 
 .. _whatsnew_0200.deprecations:
 

pandas/core/generic.py

@@ -3239,7 +3239,7 @@ def convert_objects(self, convert_dates=True, convert_numeric=False,
             a gap with more than this number of consecutive NaNs, it will only
             be partially filled. If method is not specified, this is the
             maximum number of entries along the entire axis where NaNs will be
-            filled.
+            filled. Must be greater than 0 if not None.
         downcast : dict, default is None
             a dict of item->dtype of what to downcast if possible,
             or the string 'infer' which will try to downcast to an appropriate
@@ -3257,6 +3257,9 @@ def convert_objects(self, convert_dates=True, convert_numeric=False,
     @Appender(_shared_docs['fillna'] % _shared_doc_kwargs)
     def fillna(self, value=None, method=None, axis=None, inplace=False,
                limit=None, downcast=None):
+        if is_integer(limit) and not limit > 0:
+            raise ValueError('`limit` keyword argument must be greater '
+                             'than 0.')
         if isinstance(value, (list, tuple)):
             raise TypeError('"value" parameter must be a scalar or dict, but '
                             'you passed a "{0}"'.format(type(value).__name__))
@@ -3662,7 +3665,7 @@ def replace(self, to_replace=None, value=None, inplace=False, limit=None,
             * 0: fill column-by-column
             * 1: fill row-by-row
         limit : int, default None.
-            Maximum number of consecutive NaNs to fill.
+            Maximum number of consecutive NaNs to fill. Must be greater than 0.
         limit_direction : {'forward', 'backward', 'both'}, default 'forward'
             If limit is specified, consecutive NaNs will be filled in this
             direction.
@@ -3704,6 +3707,9 @@ def interpolate(self, method='linear', axis=0, limit=None, inplace=False,
         """
         Interpolate values according to different methods.
         """
+        if is_integer(limit) and not limit > 0:
+            raise ValueError("`limit` keyword argument must be greater "
+                             "than 0.")
 
         if self.ndim > 2:
             raise NotImplementedError("Interpolate has not been implemented "

pandas/tests/series/test_missing.py

@@ -278,6 +278,11 @@ def test_fillna_raise(self):
         self.assertRaises(TypeError, s.fillna, [1, 2])
         self.assertRaises(TypeError, s.fillna, (1, 2))
 
+        # related GH 9217, make sure limit is greater than 0
+        for limit in [-1, 0]:
+            s = Series([1, 2, 3, None])
+            tm.assertRaises(ValueError, lambda: s.fillna(1, limit=limit))
+
     def test_isnull_for_inf(self):
         s = Series(['a', np.inf, np.nan, 1.0])
         with pd.option_context('mode.use_inf_as_null', True):
@@ -730,6 +735,11 @@ def test_interp_limit(self):
         result = s.interpolate(method='linear', limit=2)
         assert_series_equal(result, expected)
 
+        # GH 9217
+        for limit in [-1, 0]:
+            s = pd.Series([1, 2, np.nan, np.nan, 5])
+            tm.assertRaises(ValueError, lambda: s.interpolate(limit=limit))
+
     def test_interp_limit_forward(self):
         s = Series([1, 3, np.nan, np.nan, np.nan, 11])