added copy/deepcopy to ndframe, fixes pandas-dev#15370

Author: bmcfee

pandas/core/generic.py

@@ -3156,6 +3156,13 @@ def copy(self, deep=True):
         data = self._data.copy(deep=deep)
         return self._constructor(data).__finalize__(self)
 
+    __copy__ = copy
+
+    def __deepcopy__(self, memo=None):
+        if memo is None:
+            memo = {}
+        return self.copy(deep=True)
+
     def _convert(self, datetime=False, numeric=False, timedelta=False,
                  coerce=False, copy=True):
         """

pandas/tests/frame/test_misc_api.py

@@ -332,6 +332,15 @@ def test_deepcopy(self):
         for idx, value in compat.iteritems(series):
             self.assertNotEqual(self.frame['A'][idx], value)
 
+    def test_deepcopy_empty(self):
+        # This test covers empty frame copying with non-empty column sets
+        # as reported in issue #15370
+        # https://github.com/pandas-dev/pandas/issues/15370
+        empty_frame = DataFrame(data=[], index=[], columns=['A'])
+        empty_frame_copy = deepcopy(empty_frame)
+
+        self.assertEqual(empty_frame, empty_frame_copy)
+
     # ---------------------------------------------------------------------
     # Transposing