python 文件读与写详解

import sys,time
'''
#文件句柄
f = open("yesterday2",'a',encoding="utf-8")#'r'=read,'w'=write,w是创建文件.a=append追加的意思.默认读模式
# print(f.read())#文件光标读取一遍
f.write("我爱北京天安门.....\n")
f.write("天安门上太阳升.....")
#文件关闭
f.close()
'''
# f = open("yesterday",'r',encoding="utf-8")
# # print(f.readline())#只读一行
# for i in range(5):
#     print(f.readline())#读前5行
#
# f.close()

# f = open("yesterday",'r',encoding="utf-8")
# for line in f.readlines():
#     print(line.strip())

#low loop
# f = open("yesterday",'r',encoding="utf-8")
# for index,line in enumerate(f.readlines()):
#     if index == 9:#取第10行数据
#         print('-----分割线-----')
#         continue
#     print(line.strip())

#high bige
# count = 0
# f = open("yesterday",'r',encoding="utf-8")
# for line in f:#一行一行读，效率最高
#
#     if count == 9:#取第10行数据
#         print('-----分割线-----')
#         count += 1
#         continue
#     print(line)
#     count += 1



# f = open("yesterday",'r',encoding="utf-8")
# print(f.tell())#打印文件句柄的光标位置,按照字符计数
# print(f.readline())
# print(f.read(5))
# print(f.tell())
# f.seek(0)#光标回到0位置
# print(f.readline())
# print(f.tell())
# print(f.encoding)#打印文件编码
# print(f.fileno())
# print(f.isatty())#打印终端设备
# print(f.flush())#刷新，实时刷新到硬盘上
# f.truncate(10)#截断,从头开始截断。必须为a模式


# f = open("yesterday2",'r+',encoding="utf-8")#可读写
# # f1 = open("yesterday2",'w+',encoding="utf-8")#可写读
# # f2 = open("yesterday2",'a+',encoding="utf-8")#追加读
# # f3 = open("yesterday3",'rb')#二进制读，不能加encoding编码,网络传输必须用二进制打开
# f4 = open("yesterday3",'wb')#二进制写，不能加encoding编码,网络传输必须用二进制打开
# f4.write('hello world'.encode())#二进制写必须转换成str类型，不写就是默认utf-8模式
#
# #写读是先创建一个文件，读写是读取在后面添加写入
# print(f.readline())
# print(f.readline())
# print(f.readline())
# f.write('-------diao--------\n')
# print(f.read())
# f.close()

#flush 刷新输出
# for i in range(50):
#     sys.stdout.write("*")
#     sys.stdout.flush()
#     time.sleep(0.1)

#文件修改
f = open("yesterday2",'r',encoding="utf-8")
f_new = open("yesterday4.bak",'w',encoding="utf-8")


for line in f :
    if "我爱北京天安门" in line:
        line = line.replace('我爱北京天安门','肆意的快乐等着cindy去享受')#old -- 将被替换的子字符串。new -- 新字符串，用于替换old子字符串。max -- 可选字符串, 替换不超过 max 次
print(line)
    f_new.write(line)

f.close()
f_new.close()

with open("yesterday2",'r',encoding="utf-8") as f:#with方法走完自动关闭
    for line in f:
        print(line)

#打开两个文件
with open("yesterday2",'r',encoding="utf-8") as f, \
    open("yesterday", 'r', encoding="utf-8") as f2:
#with方法走完自动关闭
    for line in f:
        print(line)