BUG: bug when trying to display an embedded PandasObject (GH5324)

Author: jreback

doc/source/release.rst

@@ -637,6 +637,7 @@ Bug Fixes
   - C and Python Parser can now handle the more common multi-index column format
     which doesn't have a row for index names (:issue:`4702`)
   - Bug when trying to use an out-of-bounds date as an object dtype (:issue:`5312`)
+  - Bug when trying to display an embedded PandasObject (:issue:`5324`)
 
 pandas 0.12.0
 -------------

pandas/core/format.py

@@ -3,6 +3,7 @@
 
 import sys
 
+from pandas.core.base import PandasObject
 from pandas.core.common import adjoin, isnull, notnull
 from pandas.core.index import Index, MultiIndex, _ensure_index
 from pandas import compat
@@ -1486,6 +1487,8 @@ def _format(x):
                 if x is None:
                     return 'None'
                 return self.na_rep
+            elif isinstance(x, PandasObject):
+                return '%s' % x
             else:
                 # object dtype
                 return '%s' % formatter(x)

pandas/tests/test_frame.py

@@ -2356,6 +2356,21 @@ def test_constructor_error_msgs(self):
         with assertRaisesRegexp(ValueError, 'If using all scalar values, you must must pass an index'):
             DataFrame({'a': False, 'b': True})
 
+    def test_constructor_with_embedded_frames(self):
+
+        # embedded data frames
+        df1 = DataFrame({'a':[1, 2, 3], 'b':[3, 4, 5]})
+        df2 = DataFrame([df1, df1+10])
+
+        df2.dtypes
+        str(df2)
+
+        result = df2.loc[0,0]
+        assert_frame_equal(result,df1)
+
+        result = df2.loc[1,0]
+        assert_frame_equal(result,df1+10)
+
     def test_insert_error_msmgs(self):
 
         # GH 4107, more descriptive error message