Python how to remove last comma from print(string, end=“, ”)

Question

my output from a forloop is

string = \"\"
for x in something:
   #some operation
   string =  x += string 

print(string)

5
66
777

I use

Answer 1

list_1 = [5, 10, 15, 20]

new_list = []
[ new_list.append(f'({i}*{i+5})') for i in list_1 ] 
print(*new_list,sep="+") 

Output

(5*10)+(10*15)+(15*20)+(20*25)