import struct
def bmpinfo(s):
    try:
        s = struct.unpack('<ccIIIIIIHH', s)
        if s[0]==b'B' and s[1]==b'M':
            print('该图像为Windows位图\n图像大小：%s * %s\n颜色数：%s' % (s[6], s[7], s[9]))
        elif s[0]==b'B' and s[1]==b'A':
            print('该图像为OS/2位图\n图像大小：%s * %s\n颜色数：%s' % (s[6], s[7], s[9]))
        else:
            print('该文件并非位图文件（.bmp）')
    finally:
        print('finally...')
s = open(filename, 'rb').read(30)
bmpinfo(s)