How to rename the speakers in DF Pandas with a lower emphasis

  A = PD.Dataframe ([{:  1 ,  'b' :  2 , : , :  2 },  { 'd' :  1 ,  'b' :  2 , : , :  2 },  { 'd' :  1 ,  'b' :  4 , : " aa "" , :  2 }])     
 is there a way of all the names of the columns where there is a gap to the names with _, that is, the first_, for example, instead of  the first name . The speakers are many times larger, therefore, it is not a manual option.