let letter 切出来是什么

把 let letter = 1; 切成 Token，把每个词的原文用 / 拼起来输出。

玩具语言的词法规则：关键字 let if else while；标识符以字母或下划线开头；数字是连续的数位；字符串用一对双引号括起来（不含转义）；双字符运算符 >= <= == !=；单字符运算符 + - * / = < > ; ( )；空白只做分隔。

KEYWORDS = ("let", "if", "else", "while")
TWO = ("==", "!=", ">=", "<=")
ONE = "+-*/=<>;()"
SRC = 'let rate = 12;\nlet msg = "hi there";\ntotal = rate >= 3;'

import re
LINE = "let letter = 1;"
pat = re.compile(r'[A-Za-z_]\w*|\d+|"[^"]*"|==|!=|>=|<=|[+\-*/=<>;()]')
print("/".join(m.group() for m in pat.finditer(LINE)))