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

Author: wcwagner

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``, no TypeErrors raised when  ``width`` was not of integer type (: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):