Update after code review pandas-dev#1478

Tests added for deprected 'raise_on_error' kwarg & new 'errors' kwarg.
Clarified docstring for DataFrame.astype method

Author: m-charlton

pandas/core/generic.py

@@ -3075,11 +3075,12 @@ 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
+        raise_on_error : DEPRECATED use ``errors`` instead
+        errors : {'raise', 'ignore'}, default 'raise'.
+            Control raising of exceptions on invalid data for provided dtype.
+
+            - ``raise`` : allow exceptions to be raised
+            - ``ignore`` : suppress exceptions. On error return original object
 
             .. versionadded:: 0.20.0
 

pandas/core/internals.py

@@ -468,9 +468,9 @@ def _astype(self, dtype, copy=False, errors='raise', values=None,
         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)
+            invalid_arg = ("Expected value of kwarg 'errors' to be one of {}. "
+                           "Supplied value is '{}'".format(
+                               list(errors_legal_values), errors))
             raise ValueError(invalid_arg)
 
         # may need to convert to categorical

pandas/tests/frame/test_dtypes.py

@@ -523,6 +523,24 @@ def test_timedeltas(self):
         result = df.get_dtype_counts().sort_values()
         assert_series_equal(result, expected)
 
+    def test_illegal_arg_for_errors_in_astype(self):
+        # issue #14878
+
+        df = DataFrame([1, 2, 3])
+
+        with self.assertRaises(ValueError):
+            df.astype(np.float64, errors=True)
+
+    def test_depr_kwarg_produces_future_warning(self):
+        # issue #14878
+
+        df = DataFrame([1, 2, 3])
+
+        with tm.assert_produces_warning(FutureWarning):
+            df.astype(np.int8, raise_on_error=False)
+
+        df.astype(np.int8, errors='ignore')
+
 
 class TestDataFrameDatetimeWithTZ(tm.TestCase, TestData):
 

pandas/tests/test_internals.py

@@ -566,13 +566,6 @@ 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 """