编译原理----词法分析程序----python语言版

对python的应用还是不熟练，很多实用的方法没掌握，下面的程序本来是用C写的，为了练习一下python，又用python改写的，很粗糙，有bug，不过能运行出结果，嘿嘿，以后学好了python再来优化吧

# -*- coding: cp936 -*-

Keyword = ("begin","end","if","while","var","procedure","else","for","do","int","read","write")

Yunsuanfu = ('+','-','*','/','<','>','%','=')

Fenjiefu = (',',';','(',')','{','}',':')

Kongbai = (' ','\t','\n')

Number = ('0','1','2','3','4','5','6','7','8','9')



test="var a=10;\nvar b,c;\nprocedure p; \n\tbegin\n\t\tc=a+b\n\tend\n"

print test

length=len(test)



for i in range(length):

    if test[i] in Kongbai:

        continue

    if test[i] in Fenjiefu:

        print "分界符\t",test[i]

        continue

    if test[i] in Yunsuanfu:

        print "运算符\t",test[i]

        continue

    if test[i-1] in Number:

        continue

    if test[i] in Number:

        print "数字\t",

        while test[i] in Number:

            print test[i],

            i+=1

        print ''

    if test[i-1] in Number or (test[i-1]>='a' and test[i-1]<='z'):

        continue

    j=0

    temp = ""

    while True:

        if test[i] in Kongbai or test[i] in Yunsuanfu or test[i] in Fenjiefu:

            break

        else:

            j+=1

        i+=1

    temp = test[i-j:i]    

    if temp in Keyword:

        print "关键字\t",temp

    else:

        print "标识符\t",temp

2012年3月21日 22:43:52改写的代码：

 1 # -*- coding: cp936 -*-
 2 Keyword = ("begin","end","if","while","var","procedure","else","for","do","int","read","write")
 3 Yunsuanfu = ('+','-','*','/','<','>','%','=')
 4 Fenjiefu = (',',';','(',')','{','}',':')
 5 Kongbai = (' ','\t','\n')
 6 
 7 test="var a=10;\nvar b,c;\nprocedure p; \n\tbegin\n\t\tc=a+b\n\tend\n"
 8 print test
 9 length=len(test)
 i=-1
 while i < length:
     i+=1
     if test[i] in Kongbai:
         continue
     if test[i] in Fenjiefu:
         print "分界符\t",test[i]
         continue
     if test[i] in Yunsuanfu:
         print "运算符\t",test[i]
         continue
     if test[i].isdigit():
         print "数字\t",
         while test[i].isdigit():
             print test[i],
             i+=1
         print ''
         i-=1
         continue
     j=0
     temp = ""
     while True:
         if test[i] in Kongbai or test[i] in Yunsuanfu or test[i] in Fenjiefu:
             break
         else:
             j+=1
         i+=1
     temp = test[i-j:i]    
     if temp in Keyword:
         print "关键字\t",temp
     else:
         print "标识符\t",temp

     i-=1