问统计多个文件累计单词频率（python)？

import sys
import re
import os
def countfile(filename,words): #words 结果,为字典
    try:
        f = open(filename,'r',encoding='ANSI')
    except Exception as e:
        print(e)
        return 0
    txt = f.read()
    f.close()
    splitchars = set([])
    for c in txt:
        if not ('a' <= c <= 'z' or 'A' <= c <= 'Z'):
            splitchars.add(c)
    splitstr = ''
    for c in splitchars:
        if c in {'.','?','!','"',"'",'(',')','|','*','$','\\','[',']','^','{','}'}:
            splitstr += '\\'+c+'|' 
        else:
            splitstr += c+'|'
    splitstr += ' ' 
    lst = re.split(splitstr,txt)
    for x in lst:
        if x=='': 
            continue
        lx = x.lower()
        if lx in words:
            words[lx] += 1
        else:
            words[lx] = 1
    return 1
result = {}
lst = os.listdir()
for x in lst:
    if os.path.isfile(x):
        if x.lower().endwith('.txt') and x.lower().startswith('b1'): #以.txt结尾。startwith('..')以·..开始
            countfile(x,result)
lst = list(result.items())
lst.sort()
f = open(sys.argv[1],'w') 
for x in lst:
    f.write('%s\t%d\n'%(x[0],x[1]))
f.close()