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))
aW1wb3J0IHJlCiAKcmVnZXggPSByIig/PCFcZCkoKFwoKT9cZCsoPzpbLi1dXGQrKT8oPygyKVwpKSlcKlwxKD8hXGQpIgogCnRlc3Rfc3RyID0gKCI1KjUgLS0+IDUgIFxuIgoJIjMuMTQqNCAtLT4gbm8gcmV0dXJuICBcbiIKCSIoMTAtNCkqKDEwLTQpIC0tPiAoMTAtNCkiKQogCmZvciBtIGluIHJlLmZpbmRpdGVyKHJlZ2V4LCB0ZXN0X3N0cik6CglwcmludChtLmdyb3VwKDEpKQ==