day-2 python 文件读写模式r,r+,w,w+,a,a+的区别

r+和w+都是可读可写，区别在于r+读文件时，不会覆盖之前的内容，之前的内容能够读出来；w+读时，会覆盖之前的内容；所以读文件时，用r或者r+

#读操作 r

filepath = 'aa.log' #aa.log存在
#读操作
#read()方法，一次都读出来
with open(filepath,'r') as f:
    print(f.read())

C:UsersadminMiniconda3python.exe E:/python/文件读写.py
hello world!


Process finished with exit code 0

filepath = 'a.log'  #a.log不存在，执行报错
#读操作
#read()方法，一次都读出来
with open(filepath,'r') as f:
    print(f.read())

C:UsersadminMiniconda3python.exe E:/python/文件读写.py
Traceback (most recent call last):
  File "E:/python/文件读写.py", line 4, in <module>
    with open(filepath,'r') as f:
FileNotFoundError: [Errno 2] No such file or directory: 'a.log'

Process finished with exit code 1

#读写操作 r+

#r+写操作
filepath = 'aa.log'
with open(filepath, 'r+') as f:
    f.write('文字被替换成hahaha')
    print(f.read())

C:UsersadminMiniconda3python.exe E:/python/文件读写.py
被替换成hahaha

Process finished with exit code 0

#readline()读操作

filepath = 'my.log'
with open(filepath,'r',encoding='UTF-8') as f:
    print(f.readline().strip())
    print(f.readline().strip())

C:UsersadminMiniconda3python.exe E:/python/文件读写.py
2019-10-12 09:34:23,073 - E:/python/test.py[line:9] - DEBUG: 默认日志级别是debug
2019-10-12 09:34:23,075 - E:/python/test.py[line:10] - INFO: info级别

Process finished with exit code 0

#readlines()读操作,读到的内容，返回一个列表

#readlines()方法，一次都读出来，并返回一个列表
with open(filepath,'r',encoding='UTF-8') as f:
    print(f.readlines())

C:UsersadminMiniconda3python.exe E:/python/文件读写.py
['2019-10-12 默认日志级别是debug
', '2019-10-12 info级别
', '
']

Process finished with exit code 0

#将readlines读到的内容存放到line中，使用for循环遍历内容
with open(filepath,'r',encoding='UTF-8') as f:
    lines = f.readlines()
for line in lines:
    print(line.strip())

C:UsersadminMiniconda3python.exe E:/python/文件读写.py
2019-10-12 默认日志级别是debug
2019-10-12 info级别


Process finished with exit code 0

# 如果要逐行读取，直接遍历文件对象就可以了
with open(filepath,'r',encoding='UTF-8') as f:
    for line in f:
        print(line.strip())

C:UsersadminMiniconda3python.exe E:/python/文件读写.py
2019-10-12 默认日志级别是debug
2019-10-12 info级别


Process finished with exit code 0

#写操作
with open(filepath,'w',encoding='UTF-8') as f:
    f.write('hello world!
')

with open(filepath,'r',encoding='UTF-8') as f:
    print(f.read())

C:UsersadminMiniconda3python.exe E:/python/文件读写.py
hello world!


Process finished with exit code 0

#w+读写模式

with open(filepath,'w+',encoding='UTF-8') as f:
    f.write('hello world!
')
    f.seek(0)
    print(f.read())

C:UsersadminMiniconda3python.exe E:/python/文件读写.py
hello world!


Process finished with exit code 0

#a+追加读写

with open(filepath,'a+',encoding='UTF-8') as f:
    f.write('hello world!
')
    f.seek(0)
    print(f.read())

C:UsersadminMiniconda3python.exe E:/python/文件读写.py
hello world!
hello world!


Process finished with exit code 0

#读模式，只能读，不能写，默认读模式
f = open(r'E:cnzday1列表.py','r',encoding='utf-8')
result = f.read()
print(result)
f.close()

#读模式r 写模式w 追加模式a
#写模式，只能写，不能读，写模式会覆盖之前的内容

f = open('test.txt','w',encoding='utf-8')
f.write('abc')
f.close()

# 追加模式，写文件时，不会覆盖之前的内容
f = open('test.txt','a',encoding='utf-8')
# f.write('哈哈哈')
f.read()
f.close()

# 总结：
# 读模式，只能读，不能写，打开不存在的文件会报错
# 写模式，只能写，不能读，打开不存在的文件会创建
# 追加模式，只能写，不能读，在原文件基础上增加内容，打开不存在的文件，会创建
# 只要跟r有关的，打开不存在的文件，会报错
# 只要和w有关，都会清空之前的文件
# a+模式，文件指针模式是在末尾的，如果想读文件，需要seek(0)
#writelines传一个list，会把list里面的元素写到文件里

# r+       w+       a+
# 读写模式  写读模式  追加读模式

f = open('test3.txt','a+',encoding='utf-8')
f.write('哈哈哈1')
f.read()
f.close()

l = ['a','b','c','d']
f = open('test.txt','w',encoding='utf-8')
f.writelines(l)
f.close()