Python file operations [9]

Open the file mode

1. Text mode operation

r read-only mode [default]
w [write-only mode unreadable; does not exist, create; there is then emptied the contents of the original write new content;]
a append mode [unreadable; does not exist, create; there is an additional way places write new content;]

2 bytes manner

b represents the manner in bytes, no coding parameter encoding

rb byte read
wb byte write, the original content file empty
ab additional byte write

r file read
first create a file aa.txt write to

2. open () function to open a file

In [1]: f = open('./aa.txt','r')

In [2]: mm = f.read()  #一次读文全部文件到内存中
In [4]: print mm
love
123
主动关闭文件
f.close()

Circular file objects

f = open('./aa.txt')

for line in f:
    print(line)

f.close()
[root@aliyun ~]# python3 000.py 
love

123

Third, write files

1. w write

f = open('./aa.txt','w')
f.write('hello\nworld\nnihao\n')  针对文本模式的写,需要自己写换行符("\n")
f.close()
python3 000.py 
hello       #清空以前的内容 保存新内容
world
nihao

2. a Append

f = open('./aa.txt','a')
f.write('hello\nworld\nnihao\n')  针对文本模式的写,需要自己写换行符("\n")
f.close()
python3 000.py 
hello
world
nihao
hello
world
nihao
~     

Fourth, the context manager

Use context manager to open a file, you can let Python automatically closes the file object, do not write f.close ()

Use the keyword with the context manager

file_name = "a.txt"
with    open(file_name, 'r', encoding='utf-8')  as f:
    # with 语句需要缩进，当代码出了这个缩进范围， with 就会帮我们关闭这个文件对象
    for line in f:
        print(line)
print("当你看到这行文字时，with 语句，已经关闭了刚才打开的文件对象")

The following operations are text


and is the same as above