astype checks notnull Fixes: #8732

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 +2141,22 @@ def setUp(self):
         self.simple = DataFrame(arr, columns=['one', 'two', 'three'],
                                 index=['a', 'b', 'c'])
 
+    def test_hasnulls(self):
+        # Github Issue 8732
+        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)
+
+        casted = df.astype(np.str)
+        expected = DataFrame(df.values.astype(np.str),
+                             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)

vb_suite/astype.py

@@ -0,0 +1,14 @@
+from vbench.api import Benchmark
+
+common_setup = """from pandas_vb_common import *
+from datetime import timedelta
+import numpy as np
+
+N = 1000000
+arr = np.random.randint(1,10,size=1000000)
+s = pd.Series(arr)
+"""
+
+astype_test = Benchmark('s.astype(np.str)',
+                        common_setup,
+                        name='astype_test')

vb_suite/suite.py

@@ -13,6 +13,7 @@
            'indexing',
            'io_bench',
            'io_sql',
+           'astype',
            'inference',
            'hdfstore_bench',
            'join_merge',