python通过文件头判断文件类型

import struct 
 
# 支持文件类型 
# 用16进制字符串的目的是可以知道文件头是多少字节 
# 各种文件头的长度不一样，少半2字符，长则8字符 
def typeList(): 
  return { 
    "52617221": EXT_RAR,"504B0304": EXT_ZIP} 
 
# 字节码转16进制字符串 
def bytes2hex(bytes): 
  num = len(bytes) 
  hexstr = u"" 
  for i in range(num): 
    t = u"%x" % bytes[i] 
    if len(t) % 2: 
      hexstr += u"0" 
    hexstr += t 
  return hexstr.upper() 
 
# 获取文件类型 
def filetype(filename): 
  binfile = open(filename,'rb') # 必需二制字读取 
  tl = typeList() 
  ftype = 'unknown' 
  for hcode in tl.keys(): 
    numOfBytes = len(hcode) / 2 # 需要读多少字节 
    binfile.seek(0) # 每次读取都要回到文件头，不然会一直往后读取 
    hbytes = struct.unpack_from("B"*numOfBytes,binfile.read(numOfBytes)) # 一个 "B"表示一个字节 
    f_hcode = bytes2hex(hbytes) 
    if f_hcode == hcode: 
      ftype = tl[hcode] 
      break 
  binfile.close() 
  return ftype 
 
if __name__ == '__main__': 
  print filetype(Your-file-path)