BUG: closes issue #7212 - read_hdf modifying passed columns list

parameter when multi-indexed

Author: ajamian

pandas/io/pytables.py

@@ -4022,7 +4022,11 @@ def read(self, where=None, columns=None, **kwargs):
             df = concat(frames, axis=1, verify_integrity=False).consolidate()
 
         # apply the selection filters & axis orderings
-        df = self.process_axes(df, columns=columns)
+        if type(columns) is list:
+            columns_new = list(columns)
+        else:
+            columns_new = columns
+        df = self.process_axes(df, columns=columns_new)
 
         return df