1、可以在mode参数中添加'b'字符。所有适合文件对象的相同方法。然而，每种方法都希望并返回一个bytes对象。

>>> with open(`dog_breeds.txt`, 'rb') as reader:
>>>     print(reader.readline())
b'Pug\n'

2、当打开文件并单独阅读这些字节时，可以看到它确实是一个png文件:

>>> with open('jack_russell.png', 'rb') as byte_reader:
>>>     print(byte_reader.read(1))
>>>     print(byte_reader.read(3))
>>>     print(byte_reader.read(2))
>>>     print(byte_reader.read(1))
>>>     print(byte_reader.read(1))
b'\x89'
b'PNG'
b'\r\n'
b'\x1a'
b'\n'

知识点扩展：

读取文件的字节流数据，将其转换为十六进制数据

def read_file():
    with open('./flag.zip','rb') as file_byte:
        file_hex = file_byte.read().hex()
        print(file_hex)
        write_file(file_hex)

def write_file(file_hex):
    with open('new.txt','w') as new_file:
        new_file.write(file_hex)

if __name__ == '__main__':
    read_file()

读取文件的字节流数据，将其编码为base64并输出

import base64

def read_file():
    with open('./flag.zip','rb') as file_byte:
        file_base64 = base64.b64encode(file_byte.read())
        print(file_base64)

if __name__ == '__main__':
    read_file()

将十六进制文件转化为字节流文件写入

import struct

a = open("str.txt","r")#十六进制数据文件
lines = a.read()
res = [lines[i:i+2] for i in range(0,len(lines),2)]

with open("xxx.xxx","wb") as f:
	for i in res:
		s = struct.pack('B',int(i,16))
		f.write(s)