API: define __copy__ for NDFrame (pandas-dev#8571)

Author: akleeman

pandas/core/generic.py

@@ -3015,6 +3015,11 @@ def copy(self, deep=True):
         data = self._data.copy(deep=deep)
         return self._constructor(data).__finalize__(self)
 
+    # Defining these special function ensures that ``copy.copy(ndframe)`` behaves
+    # the same as ``ndframe.copy``.
+    # https://github.com/pydata/pandas/issues/8571
+    __copy__ = copy
+
     def _convert(self, datetime=False, numeric=False, timedelta=False,
                  coerce=False, copy=True):
         """

pandas/tests/frame/test_misc_api.py

@@ -2,8 +2,8 @@
 
 from __future__ import print_function
 # pylint: disable-msg=W0612,E1101
-from copy import deepcopy
 import sys
+import copy
 import nose
 from distutils.version import LooseVersion
 
@@ -330,7 +330,14 @@ def test_values(self):
         self.assertTrue((self.frame.values[:, 0] == 5).all())
 
     def test_deepcopy(self):
-        cp = deepcopy(self.frame)
+        cp = copy.deepcopy(self.frame)
+        series = cp['A']
+        series[:] = 10
+        for idx, value in compat.iteritems(series):
+            self.assertNotEqual(self.frame['A'][idx], value)
+
+    def test_copy_dot_copy(self):
+        cp = copy.copy(self.frame)
         series = cp['A']
         series[:] = 10
         for idx, value in compat.iteritems(series):

pandas/tests/series/test_misc_api.py

@@ -1,6 +1,7 @@
 # coding=utf-8
 # pylint: disable-msg=E1101,W0612
 
+import copy
 import numpy as np
 import pandas as pd
 
@@ -40,6 +41,11 @@ def test_copy_index_name_checking(self):
         printing.pprint_thing(self.ts.index.name)
         self.assertIsNone(self.ts.index.name)
 
+    def test_copy_dot_copy(self):
+        cp = copy.copy(self.ts)
+        cp[0] += 1.
+        self.assertNotEqual(cp[0], self.ts[0])
+
     def test_append_preserve_name(self):
         result = self.ts[:5].append(self.ts[5:])
         self.assertEqual(result.name, self.ts.name)