astype checks notnull Fixes: pandas-dev#8732

Author: Vikram Bhandoh

pandas/core/internals.py

@@ -398,7 +398,10 @@ def _astype(self, dtype, copy=False, raise_on_error=True, values=None,
             # force the copy here
             if values is None:
                 # _astype_nansafe works fine with 1-d only
-                values = com._astype_nansafe(self.values.ravel(), dtype, copy=True)
+                if isnull(self.values).any():
+                    values = com._astype_nansafe(self.values.ravel(), dtype, copy=True)
+                else:
+                    values = self.values.ravel().astype(dtype)
                 values = values.reshape(self.values.shape)
             newb = make_block(values,
                               ndim=self.ndim, placement=self.mgr_locs,

pandas/tests/test_frame.py

@@ -2141,6 +2141,15 @@ def setUp(self):
         self.simple = DataFrame(arr, columns=['one', 'two', 'three'],
                                 index=['a', 'b', 'c'])
 
+    def test_hasnulls(self):
+        df = tm.makeMissingDataframe()
+        self.assertEqual(df['A'].notnull().all(), False)
+        casted = df.astype(np.float64)
+        expected = DataFrame(df.values.astype(np.float64),
+                             index=df.index,
+                             columns=df.columns)
+        assert_frame_equal(casted, expected)
+
     def test_get_axis(self):
         f = self.frame
         self.assertEqual(f._get_axis_number(0), 0)