Task: converting a line from a camel register into a snake

You need to convert a line from a camel case to a snake case, add the ability to change the separator. I solved the problem, but I would like to know how to solve it more correctly.

   def   Camel_to_snake  (  str , sp =  '' ' ):  snake_register =  '' '   for  i  in   str :   if  i.isupper: : : : : : : : :  Snake_register += Sep +I.Lower ()   else :  synake_register += i  Print  (Snake_register.lstrip (SEP)) camel_register =  'thisiscamel