实际上，其他关于r+模的答案都有问题。

测试。在文件内容中:

hello1
ok2
byebye3

py脚本是:

with open("test.in", 'r+')as f:
    f.readline()
    f.write("addition")

执行它和测试。In的内容将更改为:

hello1
ok2
byebye3
addition

然而，当我们将脚本修改为:

with open("test.in", 'r+')as f:
    f.write("addition")

测试。也可以这样回答:

additionk2
byebye3

因此，如果我们不执行读取操作，r+模式将允许我们从头覆盖内容。如果我们做一些读操作，f.r ewrite()只会追加到文件中。

顺便说一下，如果我们在f.e re (write_content)之前执行f.e re (0,0)， write_content将从(0,0)位置开始覆盖它们。

假设你用一个with语句打开文件，就像你应该做的那样。然后你可以这样从你的文件中读取:

with open('somefile.txt', 'w+') as f:
    # Note that f has now been truncated to 0 bytes, so you'll only
    # be able to read data that you write after this point
    f.write('somedata\n')
    f.seek(0)  # Important: return to the top of the file before reading, otherwise you'll just read an empty string
    data = f.read() # Returns 'somedata\n'

注意f.seek(0)——如果您忘记了这一点，f.read()调用将尝试从文件末尾读取，并返回一个空字符串。

如h4z3所述， 在实际应用中， 有时你的数据太大，不能直接加载所有内容，或者你有一个生成器，或者实时传入的数据，你可以使用w+存储在一个文件中，然后读取。

下面的清单可能会有帮助

角色的意义

'r' -打开读取(默认)

'w' -打开写入，首先截断文件

'x' -打开独占创建，如果文件已经存在则失败

'a' -打开用于写入，如果存在则附加到文件的末尾

'b' -二进制模式

't' -文本模式(默认)

'+' -打开更新(读取和写入)

默认模式是'r'(用于阅读文本，'rt'的同义词)。模式'w+'和'w+b'打开并截断文件。模式'r+'和'r+b'打开文件，没有截断。

参考:https://docs.python.org/3/library/functions.html开放

文件被截断了，所以你可以调用read()(不会引发异常，不像使用'w'打开时那样)，但你会得到一个空字符串。

下面是打开文件的不同模式:

r Opens a file for reading only. The file pointer is placed at the beginning of the file. This is the default mode. rb Opens a file for reading only in binary format. The file pointer is placed at the beginning of the file. This is the default mode. r+ Opens a file for both reading and writing. The file pointer will be at the beginning of the file. rb+ Opens a file for both reading and writing in binary format. The file pointer will be at the beginning of the file. w Opens a file for writing only. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing. wb Opens a file for writing only in binary format. Overwrites the file if the file exists. If the file does not exist, creates a new file for writing. w+ Opens a file for both writing and reading. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing. wb+ Opens a file for both writing and reading in binary format. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing. a Opens a file for appending. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing. ab Opens a file for appending in binary format. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing. a+ Opens a file for both appending and reading. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing. ab+ Opens a file for both appending and reading in binary format. The file pointer is at the end of the file if the file exists. The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing.