python实现词法分析器

简单python词法分析器实现，供大家参考，具体内容如下

词法分析器状态转换图：

词法分析器总流程图：

预处理程序：

词法分析器：

词法分析器程序详细设计

详细代码实现:

#!/usr/bin/env python3.4
# coding=utf-8
import sys
import string


keywards = {}

# 关键字部分
keywards['false'] = 101
keywards['class'] = 102
keywards['finally'] = 103
keywards['is'] = 104
keywards['return'] = 105
keywards['none'] = 106
keywards['continue'] = 107
keywards['for'] = 108
keywards['lambda'] = 109
keywards['try'] = 110
keywards['true'] = 111
keywards['def'] = 112
keywards['from'] = 113
keywards['nonlocal'] = 114
keywards['while'] = 115
keywards['and'] = 116
keywards['del'] = 117
keywards['global'] = 118
keywards['not'] = 119
keywards['with'] = 120
keywards['as'] = 121
keywards['elif'] = 122
keywards['if'] = 123
keywards['or'] = 124
keywards['yield'] = 125
keywards['assert'] = 126
keywards['else'] = 127
keywards['import'] = 128
keywards['pass'] = 129
keywards['break'] = 130
keywards['except'] = 131
keywards['in'] = 132
keywards['raise'] = 133

# 符号
keywards['+'] = 201
keywards['-'] = 202
keywards['*'] = 203
keywards['/'] = 204
keywards['='] = 205
keywards[':'] = 206
keywards['<'] = 207
keywards['>'] = 208
keywards['%'] = 209
keywards['&'] = 210
keywards['!'] = 211
keywards['('] = 212
keywards[')'] = 213
keywards['['] = 214
keywards[']'] = 215
keywards['{'] = 216
keywards['}'] = 217
keywards['#'] = 218
keywards['|'] = 219
keywards[','] = 220
# 变量
# keywards['var'] = 301

# 常量
# keywards['const'] = 401

# error
# keywards['const'] = 501

signlist = {}


# 预处理函数，将文件中的空格，换行等无关字符处理掉
def pretreatment(file_name):
 try:
  fp_read = open(file_name, 'r')
  fp_write = open('file.tmp', 'w')
  sign = 0
  while true:
   read = fp_read.readline()
   if not read:
    break
   length = len(read)
   i = -1
   while i < length - 1:
    i += 1
    if sign == 0:
     if read[i] == ' ':
      continue
    if read[i] == '#':
     break
    elif read[i] == ' ':
     if sign == 1:
      continue
     else:
      sign = 1
      fp_write.write(' ')
    elif read[i] == '\t':
     if sign == 1:
      continue
     else:
      sign = 1
      fp_write.write(' ')
    elif read[i] == '\n':
     if sign == 1:
      continue
     else:
      fp_write.write(' ')
      sign = 1
    elif read[i] == '"':
     fp_write.write(read[i])
     i += 1
     while i < length and read[i] != '"':
      fp_write.write(read[i])
      i += 1
     if i >= length:
      break
     fp_write.write(read[i])
    elif read[i] == "'":
     fp_write.write(read[i])
     i += 1
     while i < length and read[i] != "'":
      fp_write.write(read[i])
      i += 1
     if i >= length:
      break
     fp_write.write(read[i])
    else:
     sign = 3
     fp_write.write(read[i])
 except exception:
  print(file_name, ': this filename not found!')


def save(string):
 if string in keywards.keys():
  if string not in signlist.keys():
   signlist[string] = keywards[string]
 else:
  try:
   float(string)
   save_const(string)
  except valueerror:
   save_var(string)


def save_var(string):
 if string not in signlist.keys():
  if len(string.strip()) < 1:
   pass
  else:
   if is_signal(string) == 1:
    signlist[string] = 301
   else:
    signlist[string] = 501


def save_const(string):
 if string not in signlist.keys():
  signlist[string] = 401


def save_error(string):
 if string not in signlist.keys():
  signlist[string] = 501


def is_signal(s):
 if s[0] == '_' or s[0] in string.ascii_letters:
  for i in s:
   if i in string.ascii_letters or i == '_' or i in string.digits:
    pass
   else:
    return 0
  return 1
 else:
  return 0


def recognition(filename):
 try:
  fp_read = open(filename, 'r')
  string = ""
  sign = 0
  while true:
   read = fp_read.read(1)
   if not read:
    break

   if read == ' ':
    if len(string.strip()) < 1:
     sign = 0
     pass
    else:
     if sign == 1 or sign == 2:
      string += read
     else:
      save(string)
      string = ""
      sign = 0
   elif read == '(':
    if sign == 1 or sign == 2:
     string += read
    else:
     save(string)
     string = ""
     save('(')
   elif read == ')':
    if sign == 1 or sign == 2:
     string += read
    else:
     save(string)
     string = ""
     save(')')
   elif read == '[':
    if sign == 1 or sign == 2:
     string += read
    else:
     save(string)
     string = ""
     save('[')
   elif read == ']':
    if sign == 1 or sign == 2:
     string += read
    else:
     save(string)
     string = ""
     save(']')
   elif read == '{':
    if sign == 1 or sign == 2:
     string += read
    else:
     save(string)
     string = ""
     save('{')
   elif read == '}':
    if sign == 1 or sign == 2:
     string += read
    else:
     save(string)
     string = ""
     save('}')
   elif read == '<':
    save(string)
    string = ""
    save('<')
   elif read == '>':
    save(string)
    string = ""
    save('>')
   elif read == ',':
    save(string)
    string = ""
    save(',')
   elif read == "'":
    string += read
    if sign == 1:
     sign = 0
     save_const(string)
     string = ""
    else:
     if sign != 2:
      sign = 1
   elif read == '"':
    string += read
    if sign == 2:
     sign = 0
     save_const(string)
     string = ""
    else:
     if sign != 1:
      sign = 2
   elif read == ':':
    if sign == 1 or sign == 2:
     string += read
    else:
     save(string)
     string = ""
     save(':')
   elif read == '+':
    save(string)
    string = ""
    save('+')
   elif read == '=':
    save(string)
    string = ""
    save('=')
   else:
    string += read

 except exception as e:
  print(e)


def main():
 if len(sys.argv) < 2:
  print("please input filename")
 else:
  pretreatment(sys.argv[1])
 recognition('file.tmp')
 for i in signlist.keys():
  print("(", signlist[i], ",", i, ")")


if __name__ == '__main__':
 main()

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。

原文链接：https://blog.csdn.net/IT_DREAM_ER/article/details/53485583