BUG: Add type check for width parameter in str.pad method GH13598

doc/source/whatsnew/v0.19.0.txt

@@ -614,3 +614,4 @@ Bug Fixes
 - Bug in ``groupby`` with ``as_index=False`` returns all NaN's when grouping on multiple columns including a categorical one (:issue:`13204`)
 
 - Bug where ``pd.read_gbq()`` could throw ``ImportError: No module named discovery`` as a result of a naming conflict with another python package called apiclient  (:issue:`13454`)
+- Bug in ``pandas.Series.str.zfill``, when ``width`` was not of integer type no ``TypeError`` was raised, which resulted in a series with all NaN values (:issue:`13598`)

pandas/core/strings.py

@@ -914,6 +914,10 @@ def str_pad(arr, width, side='left', fillchar=' '):
     if len(fillchar) != 1:
         raise TypeError('fillchar must be a character, not str')
 
+    if not isinstance(width, compat.integer_types):
+        msg = 'width must be of integer type, not {0}'
+        raise TypeError(msg.format(type(width).__name__))
+
     if side == 'left':
         f = lambda x: x.rjust(width, fillchar)
     elif side == 'right':

pandas/tests/test_strings.py

@@ -1603,6 +1603,18 @@ def test_pad_fillchar(self):
                                    "fillchar must be a character, not int"):
             result = values.str.pad(5, fillchar=5)
 
+    def test_pad_width(self):
+
+        values = Series(['1', '22', 'a', 'bb'])
+
+        result = values.str.pad(5, side='left', fillchar='0')
+        expected = Series(['00001', '00022', '0000a', '000bb'])
+        tm.assert_almost_equal(result, expected)
+
+        with tm.assertRaisesRegexp(TypeError,
+                                   "width must be of integer type, not*"):
+            result = values.str.pad('f', fillchar='0')
+
     def test_translate(self):
 
         def _check(result, expected):
@@ -1745,6 +1757,33 @@ def test_center_ljust_rjust_fillchar(self):
                                    "fillchar must be a character, not int"):
             result = values.str.rjust(5, fillchar=1)
 
+    def test_center_ljust_rjust_width(self):
+        values = Series(['a', 'bb', 'ccc', NA, 'eeeee'])
+
+        result = values.str.center(4, fillchar='X')
+        expected = Series(['XaXX', 'XbbX', 'cccX', NA, 'eeeee'])
+        tm.assert_almost_equal(result, expected)
+
+        result = values.str.ljust(4, fillchar='X')
+        expected = Series(['aXXX', 'bbXX', 'cccX', NA, 'eeeee'])
+        tm.assert_almost_equal(result, expected)
+
+        result = values.str.rjust(4, fillchar='X')
+        expected = Series(['XXXa', 'XXbb', 'Xccc', NA, 'eeeee'])
+        tm.assert_almost_equal(result, expected)
+
+        with tm.assertRaisesRegexp(TypeError,
+                                   "width must be of integer type, not*"):
+            result = values.str.center('f', fillchar='X')
+
+        with tm.assertRaisesRegexp(TypeError,
+                                   "width must be of integer type, not*"):
+            result = values.str.ljust('f', fillchar='X')
+
+        with tm.assertRaisesRegexp(TypeError,
+                                   "width must be of integer type, not*"):
+            result = values.str.rjust('f', fillchar='X')
+
     def test_zfill(self):
         values = Series(['1', '22', 'aaa', '333', '45678'])
 
@@ -1767,6 +1806,17 @@ def test_zfill(self):
         expected = Series(['00001', np.nan, '00aaa', np.nan, '45678'])
         tm.assert_series_equal(result, expected)
 
+    def test_zfill_width(self):
+        values = Series(['1', '22', 'ccc', NA, 'eeeee'])
+
+        result = values.str.zfill(5)
+        expected = Series(['00001', '00022', '00ccc', NA, 'eeeee'])
+        tm.assert_almost_equal(result, expected)
+
+        with tm.assertRaisesRegexp(TypeError,
+                                   "width must be of integer type, not*"):
+            result = values.str.zfill('f')
+
     def test_split(self):
         values = Series(['a_b_c', 'c_d_e', NA, 'f_g_h'])