day08文件的操作(0221)

#1、文件操作之追加数据01：
f = open("yesterday01",'a+U',encoding="utf-8")
#a= append,追加之意，w则为写入并覆盖，r为只读,+表示可同时读写，
# U表示在读取时，可以将
 
 
自动转换为
,如 r+U,b表示处理的是二进制文件（如ftp需用rb,wb）

f.write("
when i was young I like to listen to the radio
")
data = f.read()
print(data)
f.close()

#2、文件操作之读前3行的数据：
f = open("yesterday01","r",encoding="utf-8")
for i in range(3):
    print(f.readline())

#3、打印所有的行：
f = open("yesterday01","r",encoding="utf-8")
for line in f.readlines():
    print(line)

#4、以下的作用待查：
f = open("yesterday01","r",encoding="utf-8")
for line in f.readlines():
    #print(f.readline())
    print(f.tell())
    f.seek(2)
    print(f.readline())

#5、打印出修改的内容并写入备份的文档中：
f = open("yesterday01","r+",encoding="utf-8")
f_bak = open("yesterday01bak","a+",encoding="utf-8")

for line in f.readlines():   #注意是带s的，()表示所有
    if "raddio" in line:
        line = line.replace("raddio","MP3")
        f_bak.write(line)
        print (line)
f.close()
f_bak.close()

#6、回车键：
f = open("yesterday01","a+",encoding="utf-8")
f.write("---hello------
")
f.write("---hello------
")
f.write("---hello------
")

#7、？？：
import sys
f = open("yesterday01","r+",encoding="utf-8")
f_bak = open("yesterday01bak","a+",encoding="utf-8")
find_str = sys.argv[1]
replace_str = sys.argv[2]
for line in f.readlines():
    if find_str in line:
        line = line.replace(find_str,replace_str)
        f_bak.write(line)
        print (line)
f.close()
f_bak.close()

#8、不需要用close关闭文件的方法(读最前面的42个字符，不足一行则显示一行的内容)：
with open("yesterday01","r+",encoding="utf-8") as f:
    for line in f.readlines(42):
        print (line)