Pythonはネットフレームなどのバイトファイルを処理する——CRC 8検査

#!/usr/bin/python
# -*- coding: utf-8 -*-


def crc8(line_):
    #    010101   ，  'f'     6      0x0   ，      '0b'
    line_ = bin(int('f' + line_, 16))[6:]
    # print line_
    reg = 0
    for bit in line_:
        if reg & 0x80 != 0:
            reg <<= 1
            #            reg    8bit
            reg &= 0xff
            if bit == '1':
                reg += 1
                reg &= 0xff
            reg ^= 0x07
        else:
            reg <<= 1
            reg &= 0xff
            if bit == '1':
                reg += 1
                reg &= 0xff
        # print reg
        # break
    return reg & 0xff


#         ，         "aaaaaaaaaaab00000463adc"    
filename = "ch03_mac_frame_data"
content = ""
with open(filename, "rb") as f:
    while True:
        #             （        ！！），   16     
        c = f.read(1)
        if not c:
            break
        byte = hex(ord(c))
        #  0x8       0x08     
        if len(byte) == 3:
            # print 'original byte:', byte
            byte = '0x0' + byte[2]
        # print byte
        #      0x
        content += byte[2:4]
        # print type(hex(ord(c)))

# print content

#         ，aaaaaaaaaaaaaaab        
result = content.split("aaaaaaaaaaaaaaab")[1:5]
# print len(result)
for line in result:
    #         （                    ，      ，   care）
    print
    # print line
    #   crc-8  
    print "  crc-8  :"
    if crc8(line) != 0:
        print "      ！"
    else:
        print "        ！"
    print "  MAC  ：", line[0:12]
    print " MAC  ：", line[12:24]
    print "  ：", line[24:28]
    #  "aaaa"           ，ascii  
    text = line[28:len(line) - 4]
    real_text = ""
    for i in range(0, len(text), 2):
        # text 16        ， "aaad16b6"，       ， "aa"，     ，  chr()    ascii           
        cc = int(text[i:i + 2], 16)
        character = chr(cc)
        real_text += character
    print "  ：", real_text
    print "FCS：", line[len(line) - 4:len(line)]

主に注意が必要なのはbin()・chr()・ord()・hex()これらの関数の使用です.