import re
 
regex = r"(?<!\d)((\()?\d+(?:[.-]\d+)?(?(2)\)))\*\1(?!\d)"
 
test_str = ("5*5 --> 5  \n"
	"3.14*4 --> no return  \n"
	"(10-4)*(10-4) --> (10-4)")
 
for m in re.finditer(regex, test_str):
	print(m.group(1))