Python determines upload file type

When developing upload services, it is often necessary to filter uploaded files.

This article provides you with a python method to determine the file type through the file header, which is very practical.

The code is as follows

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
  #不要忘记关闭打开的文件，避免出现异常
  binfile.close() 
  return ftype
  
if __name__ == '__main__': 
  print filetype('pythontab.jpg')

File headers of common file formats

File format file header (hex)

JPEG (jpg) FFD8FF

PNG (png) 89504E47

GIF (gif) 47494638

TIFF ( tif) 49492A00

Windows Bitmap (bmp) 424D

CAD (dwg) 41433130

Adobe Photoshop (psd) 38425053

Rich Text Format (rtf) 7B5C727466

XML (xml) 3C3F786D6C

HTML (html) 68746D6C3E

Email [thorough only] (eml) 44656C69766572792D646174653A

Outlook Express (dbx) CFAD12FEC5FD746F

Outlook (pst) 2142444E

MS Word/Excel (xls.or.doc) D0CF11 E0

MS Access (mdb) 5374616E64617264204A