| import operator | |
| import re | |
| CALC_RE = re.compile(r"\s*(-?\d+(?:\.\d+)?)\s*([+\-*/])\s*(-?\d+(?:\.\d+)?)\s*") | |
| OPS = {"+": operator.add, "-": operator.sub, "*": operator.mul, "/": operator.truediv} | |
| def calc(expr): | |
| m = CALC_RE.fullmatch(expr) | |
| if not m: | |
| return None | |
| a, op, b = float(m.group(1)), m.group(2), float(m.group(3)) | |
| if op == "/" and b == 0: | |
| return "Can't divide by zero." | |
| r = OPS[op](a, b) | |
| return str(int(r)) if r == int(r) else f"{r:.4f}".rstrip("0") |