python计算字符串长度(中文算2个字符)

txt = '名字12' 
lenTxt = len(txt) 
lenTxt_utf8 = len(txt.encode('utf-8')) 
size = int((lenTxt_utf8 - lenTxt)/2 + lenTxt)

print("size = " , size ," ,utf8 = ",lenTxt_utf8," ,len = " ,lenTxt)  # size = 6, utf8 = 8 ,len = 4