Fix syntax for Python 2.6.
Fix syntax for Python 2.6.

basho/riak-python-client,basho/riak-python-client,bmess/riak-python-client,GabrielNicolasAvellaneda/riak-python-client,bmess/riak-python-client,GabrielNicolasAvellaneda/riak-python-client,basho/riak-python-client