Fix py2.6 compatibility
Fix py2.6 compatibility

pombredanne/dask,jayhetee/dask,blaze/dask,ContinuumIO/dask,wiso/dask,gameduell/dask,vikhyat/dask,vikhyat/dask,jakirkham/dask,clarkfitzg/dask,cpcloud/dask,ContinuumIO/dask,ssanderson/dask,chrisbarber/dask,pombredanne/dask,mraspaud/dask,PhE/dask,jayhetee/dask,clarkfitzg/dask,jcrist/dask,jcrist/dask,mrocklin/dask,mraspaud/dask,cowlicks/dask,jakirkham/dask,dask/dask,mikegraham/dask,ssanderson/dask,PhE/dask,mrocklin/dask,simudream/dask,simudream/dask,blaze/dask,dask/dask,wiso/dask