BUG: improper MultiIndex conversion issue. close #2200

Author: wesm

RELEASE.rst

@@ -94,6 +94,9 @@ pandas 0.9.1
   - Pass through timezone information when calling DataFrame.align (#2127)
   - Properly sort when joining on datetime64 values (#2196)
   - Fix indexing bug in which False/True were being coerced to 0/1 (#2199)
+  - Many unicode formatting fixes (#2201)
+  - Fix improper MultiIndex conversion issue when assigning
+    e.g. DataFrame.index (#2200)
 
 pandas 0.9.0
 ============

pandas/core/index.py

@@ -2438,8 +2438,15 @@ def _ensure_index(index_like):
         return Index(index_like, name=index_like.name)
 
     if isinstance(index_like, list):
-        if len(index_like) and isinstance(index_like[0], (list, np.ndarray)):
+        klasses = (list, np.ndarray)
+        all_arrays = all(isinstance(x, klasses) for x in index_like)
+
+        if len(index_like) > 0 and all_arrays:
             return MultiIndex.from_arrays(index_like)
+        else:
+            # #2200 ?
+            index_like = [tuple(x) if isinstance(x, klasses) else x
+                          for x in index_like]
 
     return Index(index_like)
 

pandas/core/internals.py

@@ -506,10 +506,12 @@ def is_mixed_dtype(self):
 
     def set_axis(self, axis, value):
         cur_axis = self.axes[axis]
+        value = _ensure_index(value)
+
         if len(value) != len(cur_axis):
             raise Exception('Length mismatch (%d vs %d)'
                             % (len(value), len(cur_axis)))
-        self.axes[axis] = _ensure_index(value)
+        self.axes[axis] = value
 
         if axis == 0:
             for block in self.blocks:

pandas/tests/test_multilevel.py

@@ -1578,6 +1578,22 @@ def test_multiindex_na_repr(self):
         idf = df3.set_index(['A' * 30, 'C' * 30])
         repr(idf)
 
+    def test_assign_index_sequences(self):
+        # #2200
+        df = DataFrame({"a":[1,2,3],
+                        "b":[4,5,6],
+                        "c":[7,8,9]}).set_index(["a","b"])
+        l = list(df.index)
+        l[0]=("faz","boo")
+        df.index = l
+        repr(df)
+
+        # this travels an improper code path
+        l[0] = ["faz","boo"]
+        df.index = l
+        repr(df)
+
+
 if __name__ == '__main__':
 
     # unittest.main()