BUG: fix concatenate bug causing #2057, but obscured by omitted asser…

…ts. close #2057

pandas/core/common.py

@@ -885,8 +885,7 @@ def is_list_like(arg):
 def _is_sequence(x):
     try:
         iter(x)
-        assert(not isinstance(x, basestring))
-        return True
+        return not isinstance(x, basestring) and True
     except Exception:
         return False
 

pandas/core/internals.py

@@ -23,8 +23,11 @@ def __init__(self, values, items, ref_items, ndim=2):
         if issubclass(values.dtype.type, basestring):
             values = np.array(values, dtype=object)
 
-        assert(values.ndim == ndim)
-        assert(len(items) == len(values))
+        if values.ndim != ndim:
+            raise AssertionError('Wrong number of dimensions')
+
+        if len(items) != len(values):
+            raise AssertionError('Wrong number of items passed')
 
         self._ref_locs = None
         self.values = values

pandas/tools/merge.py

@@ -1025,7 +1025,7 @@ def _get_reindexed_data(self):
 
     def _concat_blocks(self, blocks):
         values_list = [b.values for b in blocks if b is not None]
-        concat_values = com._concat_compat(values_list)
+        concat_values = com._concat_compat(values_list, axis=self.axis)
 
         if self.axis > 0:
             # Not safe to remove this check, need to profile