130242014057 周陈清第2次实验

时间：2017-10-28 21:05:10 阅读：188 评论：0 收藏：0 [点我收藏+]

标签：结构图 except ima init nta ace val none 结果

代码：

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=type
self.value=value
def __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=text
self.pos=0
self.current_char=self.text[self.pos]

def error(self):
raise Exception(‘Invalid Char‘)

def advance(self):
#往下走，取值
self.pos+=1
if self.pos>len(self.text)-1:
self.current_char=None
else:
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=lexer
self.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_token
if token.type==INTEGER:
self.eat(INTEGER)
return token.value
elif token.type==LPAREN:
self.eat(LPAREN)
result=self.expr()
self.eat(RPAREN)
return result

def term(self):
result=self.factor()
while self.current_token.type in (MUL,DIV):
token=self.current_token
if token.type==MUL:
self.eat(MUL)
result=result*self.factor()
if token.type==DIV:
self.eat(DIV)
result=result/self.factor()
return result
def expr(self):
result=self.term()
while self.current_token.type in (PLUS,MINUS):
token=self.current_token
if token.type==PLUS:
self.eat(PLUS)
result=result+self.term()
if token.type==MINUS:
self.eat(MINUS)
result=result-self.term()
return result

def main():
while True:
try:
text=input(‘calc_> ‘)
except EOFError:
break
if not text:
continue
lexer=Lexer(text)
result=Interpreter(lexer).expr()
print(result)

if __name__==‘__main__‘:
main()

实验结果：

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