# coding: UTF-8#编码格式
INTEGER,PLUS,MINUS,MUL,DIV,LPAREN,RPAREN,EOF=('INTEGER','PLUS','MINUS','MUL','DIV','LPAREN','RPAREN','EOF')class Token(object):def  __init__(self,type,value):self.type=typeself.value = valuedef __str__(self):return 'Token({type},{value})'.format(type = self.type,value = self.value)class Lexer(object):
# 词法分析器
# 给每个词打标记def __init__(self, text):self.text=textself.pos=0self.current_char=self.text[self.pos]def error(self):raise Exception('Invalid Char')def advance(self):#往下走，取值self.pos+=1if self.pos>len(self.text)-1:self.current_char=Noneelse:self.current_char=self.text[self.pos]def integer(self):#多位整数处理result=''while self.current_char is not None and self.current_char.isdigit():result=result+self.current_char#往下走，取值self.advance()return int(result)def deal_space(self):while self.current_char is not None and self.current_char.isspace():self.advance()def get_next_token(self):#打标记:1）pos+1,2）返回Token(类型，数值）while self.current_char is not None:if self.current_char.isspace():self.deal_space()if self.current_char.isdigit():return Token(INTEGER,self.integer())if self.current_char=='+':self.advance()return Token(PLUS,'+')if self.current_char=='-':self.advance()return Token(MINUS,'-')if self.current_char=='*':self.advance()return Token(MUL, '*')if self.current_char=='/':self.advance()return Token(DIV, '/')if self.current_char=='(':self.advance()return Token(LPAREN, '(')if self.current_char==')':self.advance()return Token(RPAREN, ')')self.error()return Token(EOF,None)class Interpreter(object):
#句法分析
#语法树def __init__(self,lexer):self.lexer=lexerself.current_token=self.lexer.get_next_token()def error(self):raise Exception('Invalid Syntax')def eat(self,token_type):if self.current_token.type==token_type:self.current_token=self.lexer.get_next_token()else:self.error()def factor(self):token=self.current_tokenif token.type==INTEGER:self.eat(INTEGER)return token.valueelif token.type==LPAREN:self.eat(LPAREN)result=self.expr()self.eat(RPAREN)return resultdef term(self):result=self.factor()while self.current_token.type in (MUL,DIV):token=self.current_tokenif token.type==MUL:self.eat(MUL)result=result*self.factor()if token.type==DIV:self.eat(DIV)result=resultlf.factor()return resultdef expr(self):result=self.term()while self.current_token.type in (PLUS,MINUS):token=self.current_tokenif token.type==PLUS:self.eat(PLUS)result=result+self.term()if token.type==MINUS:self.eat(MINUS)result=result-self.term()return resultdef main():while True:try:text=input('calc_> ')except EOFError:Interpreter.error()breakif not text:continuelexer=Lexer(text)result=Interpreter(lexer).expr()if(result is not None):print(result)if __name__ == '__main__':main()