BUG: Fix wrong str.format() calls in Index.summary

GH3869

Author: jtratner

doc/source/release.rst

@@ -1039,6 +1039,8 @@ pandas 0.10.1
   - Fix Period resampling bug when all values fall into a single bin (:issue:`2070`)
   - Fix buggy interaction with usecols argument in read_csv when there is an
     implicit first index column (:issue:`2654`)
+  - Fix bug in ``Index.summary()`` where string format methods were being called incorrectly.
+    (:issue:`3869`)
 
 
 pandas 0.10.0

pandas/core/index.py

@@ -310,10 +310,12 @@ def _has_complex_internals(self):
     def summary(self, name=None):
         if len(self) > 0:
             head = self[0]
-            if hasattr(head,'format'):
+            if hasattr(head,'format') and\
+               not isinstance(head, compat.string_types):
                 head = head.format()
             tail = self[-1]
-            if hasattr(tail,'format'):
+            if hasattr(tail,'format') and\
+               not isinstance(tail, compat.string_types):
                 tail = tail.format()
             index_summary = ', %s to %s' % (com.pprint_thing(head),
                                             com.pprint_thing(tail))

pandas/tests/test_index.py

@@ -418,6 +418,12 @@ def test_is_all_dates(self):
 
     def test_summary(self):
         self._check_method_works(Index.summary)
+        # GH3869
+        ind = Index(['{other}%s',"~:{range}:0"], name='A')
+        result = ind.summary()
+        # shouldn't be formatted accidentally.
+        self.assert_('~:{range}:0' in result)
+        self.assert_('{other}%s' in result)
 
     def test_format(self):
         self._check_method_works(Index.format)