ENH: allow single str input to na_values #1944

Author: changhiskhan

pandas/core/common.py

@@ -775,6 +775,8 @@ def is_float_dtype(arr_or_dtype):
         tipo = arr_or_dtype.dtype.type
     return issubclass(tipo, np.floating)
 
+def is_list_like(arg):
+    return hasattr(arg, '__iter__') and not isinstance(arg, basestring)
 
 _ensure_float64 = _algos.ensure_float64
 _ensure_int64 = _algos.ensure_int64

pandas/io/parsers.py

@@ -490,6 +490,8 @@ def __init__(self, f, delimiter=None, dialect=None, names=None, header=0,
                     na_values[k] = v
             self.na_values = na_values
         else:
+            if not com.is_list_like(na_values):
+                na_values = [na_values]
             na_values = set(list(na_values))
             if keep_default_na:
                 na_values = na_values | _NA_VALUES

pandas/io/tests/test_parsers.py

@@ -532,6 +532,9 @@ def test_custom_na_values(self):
                          skiprows=[1])
         assert_almost_equal(df2.values, expected)
 
+        df3 = read_table(StringIO(data), sep=',', na_values='baz',
+                         skiprows=[1])
+        assert_almost_equal(df3.values, expected)
 
     def test_skiprows_bug(self):
         # GH #505