#-*-coding:utf-8-*-
import struct 

class bmpinfo(dict):

    def __init__(self, filepath):
        with open(filepath, 'rb') as f:
            bmp_type = f.read(2)
            bmp_type = ''.join(map(bytes.decode, struct.unpack('<cc', bmp_type)))
            if bmp_type not in ('BM', 'BA'):
                raise FormatError('%s is not bmp format' %filepath)
            if bmp_type == 'BM':
                self['windows_bmp'] = True
            else:
                self['mac_bmp'] = True
            bype_contents = f.read(28)
            self._initial_attributes(bype_contents)

    def _initial_attributes(self, byte_contents):
        infos = struct.unpack('<IIIIIIHH', byte_contents)
        self['size'] = infos[0]
        self['width'] = infos[4]
        self['height'] = infos[5]
        self['depth'] = infos[7]

    def __getattr__(self, name):
        if name not in self:
            return None
        return self[name]

info = bmpinfo('test.bmp')
print('size:%s, dept:%s' %(info.size, info.depth))