Set the default mode to 'r' in read_hdf

Author: frexvahi

pandas/io/pytables.py

@@ -313,7 +313,7 @@ def read_hdf(path_or_buf, key=None, **kwargs):
 
         """
 
-    if kwargs.get('mode', 'a') not in ['r', 'r+', 'a']:
+    if kwargs.setdefault('mode', 'r') not in ['r', 'r+', 'a']:
         raise ValueError('mode {0} is not allowed while performing a read. '
                          'Allowed modes are r, r+ and a.'
                          .format(kwargs.get('mode')))