python--基础4 （文件操作）

python文件操作步骤

#第一步：调用文件
f=open(r'D:\untitled\venv\Include\blacklist.txt', 'r', encoding='gbk')
#第二部：使用文件
print(f.readlines())
#第三部：关闭文件
f.close()

#python中内置函数with可以自动关闭文件：
with open(r'D:\untitled\venv\Include\blacklist.txt', 'r', encoding='utf-8')as f:
    print(f.readlines())

三种调用文件的路径的写法

open(r'D:\untitled\venv\Include\blacklist.txt')  #r --read  只读，代表' '内的字符串没有其他含义不进行转义
open('D:\\untitled\\venv\\Include\\blacklist.txt')
open('D:/untitled/venv/Include/blacklist.txt')

读(rt)

read读取全部内容

f.read(int)可指定参数int， ‘rt’ --->参数int代表读取int个字符 'rb'--->参数int代表读取int个字节

with open(r'D:\untitled\venv\Include\blacklist.txt', 'r', encoding='gbk')as f:
    print(f.read())

...运行结果

艾妮
你好
hello
world

readline按行读取

with open(r'D:\untitled\venv\Include\blacklist.txt', 'r', encoding='gbk')as f:
    print(f.readline(2))

...运行结果

艾妮

readlines把内容以列表形式展现

with open(r'D:\untitled\venv\Include\blacklist.txt', 'r', encoding='gbk')as f:
    print(f.readlines())

...运行结果

['艾妮\n', '你好\n', 'hello\n', 'world\n']

覆盖写（wt）

with open(r'D:\untitled\venv\Include\blacklist.txt', 'w', encoding='utf-8')as f:
    f.write('你好不好')
with open(r'D:\untitled\venv\Include\blacklist.txt', 'r', encoding='utf-8')as f:
    print(f.readlines())

...运行结果

['你好不好']

追加写appand（at）

with open(r'D:\untitled\venv\Include\blacklist.txt', 'a', encoding='utf-8')as f:
    f.write('艾妮'+'\n')
with open(r'D:\untitled\venv\Include\blacklist.txt', 'r', encoding='utf-8')as f:
    print(f.read())

...运行结果

你好不好
艾妮
艾妮
艾妮

(rb,wb,ab)

rb:read bytes 二进制字节方式读取
wb:write bytes 二进制字节方式覆盖写
ab:appand bytes 二进制字节方式追加写

示例：

with open(r'D:\untitled\venv\Include\blacklist.txt', 'wb')as f:
    f.write('艾妮'.encode('utf-8'))
with open(r'D:\untitled\venv\Include\blacklist.txt', 'ab')as f:
    f.write('艾妮'.encode('utf-8'))
with open(r'D:\untitled\venv\Include\blacklist.txt', 'rb')as f:
    print(f.read())
    f.seek(0,0)       #把光标移动到开头
    print(f.read().decode('utf-8'))

...运行结果

b'\xe8\x89\xbe\xe5\xa6\xae\xe8\x89\xbe\xe5\xa6\xae'
艾妮艾妮

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文件的光标移动

f.seek(0,0) 后面的0代表把光标移动到开头
f.seek(0,1) 后面的1代表相对位置
f.seek(0,2) 后面的2代表把光标移动到末尾

示例：# tail -f message | grep '404'

import time
with open(r'C:\Users\Administrator.USER-20190512NQ\Desktop\a.txt', 'rb') as f:
    f.seek(0, 2)
    while True:
        data = f.read()
        if b'404' in data:
            print(data.decode('utf-8'))
        else:
            time.sleep(0.2)

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