如何用python写一个简单的词法分析器

#保留字
key_word = ['abstract','assert','boolean','break','byte',
      'case','catch','char','class','const',
      'continue','default','do','double','else',
      'enum','extends','final','finally','float',
      'for','goto','if','implements','import',
      'instanceof','int','interface','long','native',
      'new','package','private','protected','public',
      'return','short','static','strictfp','super',
      'switch','synchronized','this','throw','throws',
      'transient','try','void','volatile','while']

#运算符
operator = ['+','-','*','/','%','++','--','+=','-=','+=','/=',#算术运算符
      '==','!=','>','<','>=','<=',#关系运算符
      '&','|','^','~','<<','','>',#位运算符
      '&&','||','!',#逻辑运算符
      '=','+=','-=','*=','/=','%=','<<=','=','&=','^=','|=',#赋值运算符
      '"htmlcode">

#界符
delimiters = ['{','}','[',']','(',')','.',',',':',';']


4.预处理
用正则表达式把注释去掉,在把多余的空行去掉


#预处理
def filterResource(file,new_file):
  f2 = open(new_file,'w+')
  txt = ''.join(open(file,'r').readlines())
  deal_txt = re.sub(r'\/\*[\s\S]*\*\/|\/\/.*','',txt) 
  for line in deal_txt.split('\n'):
      line = line.strip()
      line = line.replace('\\t','')
      line = line.replace('\\n','')
      if not line:
        continue
      else:
        f2.write(line+'\n')
  f2.close()
  return sys.path[0]+'\\'+ new_file


5.逐行扫描
按照刚刚的思路进行判断，把每一行的单词，添加到word_line列表中，最后在把每一行添加到token列表中。


def Scan(file):
  lines = open(file,'r').readlines()
  for line in lines:
    word = ''
    word_line = []
    i = 0
    while i <len(line):
      word +=line[i]
      if line[i]==' ' or line[i] in delimiters or line[i] in operator:
        if word[0].isalpha() or word[0]=='$' or word[0]=='_':
          word = word[:-1]
          if searchReserve(word):
            # 保留字
            word_line.append({word[:-1]:key_word.index(word)})
          else:
            # 标识符
            identifier.append({word:-2})
            word_line.append({word:-2})
        # 常数
        elif word[:-1].isdigit():
          word_line.append({word:-1})
        #else:
          #error_word.append(word)
        # 字符是界符
        if line[i] in delimiters:
          word_line.append({line[i]:len(key_word)+delimiters.index(line[i])})
        # 字符是运算符
        elif line[i] in operator:
          s = line[i] +line[i+1]
          if s in operator:
            word_line.append({s:len(key_word)+len(delimiters)+operator.index(s)})
            i +=1
          else:
            word_line.append({line[i]:len(key_word)+len(delimiters)+operator.index(line[i])})
        word = ''
      i+=1
    token.append(word_line)


6.根据单词返回是什么类型
按照保留字--界符--运算符--常数的顺序来当识别码。常数识别码是-1，标识符识别码是-2


def check(number):
  hanzi = ''
  q = len(key_word)
  w = len(delimiters)
  e = len(operator)
  if 0<number<=q:
    hanzi = '保留字'
  elif q<number <= q+w:
    hanzi = '界符'
  elif q+w<number <=q+w+e:
    hanzi = '运算符'
  elif number == -1:
    hanzi ='常数'
  elif number == -2:
    hanzi ='标识符'
  return hanzi


7. 用thinker写一个简单的界面
导入


from tkinter import * 
from tkinter.filedialog import askdirectory,askopenfilename




root = Tk()
  root.title('词法分析')
  root.resizable(0, 0)
  path = StringVar() 
  Label(root,text = "目标路径:").grid(row = 0, column = 0) 
  Entry(root, textvariable = path).grid(row = 0, column = 1) 
  Button(root, text = "路径选择", command = openfiles).grid(row = 0, column = 2)
  Button(root,text='词法分析',command= open_excel).grid(row = 0,column = 3)
  root.mainloop()


打开文件


def openfiles():
  fname = askopenfilename(title='打开文件', filetypes=[('All Files', '*')])
  path.set(fname)



简单的界面
8.导入到excel表中
需要安装包xwings


pip install xwings


导入


import xlwings as xw


把token里的单词，按照 单词 ---- 识别码 ---类型 打印到excel表中


def open_excel():
  # 预处理
  row,col=0,0
  if path.get()!='':

    txt = java_analysis.filterResource(path.get(),new_file)
    print(txt)
    #扫描
    java_analysis.Scan(txt)
    app = xw.App(visible=True,add_book=False)
    wb =app.books.open(sys.path[0]+'\\'+'test.xlsx')
    sheet = wb.sheets.active
    sheet.clear() 
    print(java_analysis.token)
    for i in range(len(java_analysis.token)):
      sheet[row,0].value = '第'+str(i+1)+'行'
      row +=1
      for word in java_analysis.token[i]:
        for k,w in word.items():
          sheet[row,3].value = k
          sheet[row,5].value = w
          sheet[row,7].value = java_analysis.check(w)
        row +=1
    sheet.autofit()#整个sheet自动调整
    #wb.save()


最后就像这样

效果
代码很烂，不过也算是大致明白词法分析器了。
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。