import res = 'birthday is 1991-11-19'res1 = re.sub('(\d{4})-(\d{2})-(\d{2})',r'\2/\3/\1',s)res2 = re.sub('(?P
     
      \d{4})-(?P
      
       \d{2})-(?P
       
        \d{2})',r'\g
        
         /\g
         
          /\g
          
           ',s)print(res1)print(res2)