python scripting

I have extracted field output from ABAQUS odb file and I want to take log of that field. In ABAUQS scripting manual, in section 9.8.2 it has been mentioned that

               log10(field output)= field output

 When I am trying to do this compilation gives me error. "a float value required"

Please guide me if i am making any mistake

Also if possible, suggest how can I get rid of this problem?