import struct

def isBMP(f):
    with open(f,'rb') as f:
        test = f.read()
    test = test[:30]
    test = struct.unpack('<ccIIIIIIHH', test)
    if test[0]==b'B' and test[1]==b'M':
        print('pic size: %d*%d'%(test[6],test[7]))
        print('color: %d'%(test[-1]))
    else:
        print('file not BMP')


f = '/Users/Jason/Desktop/test.bmp'
f2 = '/Users/Jason/Desktop/re.py'
isBMP(f)
isBMP(f2)