Check & unit test added for validity of arguments to 'errors' kwarg. Docstrings

to astype clarified.

Author: m-charlton

pandas/core/generic.py

@@ -3075,9 +3075,14 @@ def astype(self, dtype, copy=True, errors='raise', **kwargs):
             the same type. Alternatively, use {col: dtype, ...}, where col is a
             column label and dtype is a numpy.dtype or Python type to cast one
             or more of the DataFrame's columns to column-specific types.
+        raise_on_error : raise on invalid input. DEPRECATED use ``errors``
+            instead
         errors : {'raise', 'ignore'}, default 'raise'
             - ``raise`` : allow exceptions to be raised on invalid input
             - ``ignore`` : suppress raising exceptions on invalid input
+
+            .. versionadded:: 0.20.0
+
         kwargs : keyword arguments to pass on to the constructor
 
         Returns

pandas/core/internals.py

@@ -465,6 +465,13 @@ def _astype(self, dtype, copy=False, errors='raise', values=None,
         Coerce to the new type (if copy=True, return a new copy)
         raise on an except if raise == True
         """
+        errors_legal_values = ('raise', 'ignore')
+
+        if errors not in errors_legal_values:
+            invalid_arg = "Expected value of kwarg 'errors' to be one of %s. "\
+                "Supplied value is '%s'" % (', '.join("'%s'" % arg for arg in
+                                            errors_legal_values), errors)
+            raise ValueError(invalid_arg)
 
         # may need to convert to categorical
         # this is only called for non-categoricals

pandas/tests/test_internals.py

@@ -566,6 +566,13 @@ def test_astype(self):
             else:
                 self.assertEqual(tmgr.get('d').dtype.type, t)
 
+    def test_illegal_arg_for_errors_in_astype(self):
+        """ ValueError exception raised when illegal value used for errors """
+        mgr = create_mgr('a,b,c: i8')
+
+        with self.assertRaises(ValueError):
+            mgr.astype(np.float64, errors=True)
+
     def test_convert(self):
         def _compare(old_mgr, new_mgr):
             """ compare the blocks, numeric compare ==, object don't """