如何在一个变量中同时在python中以读取和追加模式打开文件 [英] how to open file in read and append mode in python at the same time in one variable

问题描述

'r'将读取文件，'w'将从头开始在文件中写入文本，而'a'将追加.如何打开文件以同时阅读和追加?

'r' will read a file, 'w' will write text in the file from the start, and 'a' will append. How can I open the file to read and append at the same time?

我尝试了这些，但是出现了错误:

I tried these, but got errors:

open("filename", "r,a")

open("filename", "w")
open("filename", "r")
open("filename", "a")

错误:

invalid mode: 'r,a'

推荐答案

您正在寻找r+或a+模式，该模式允许对文件进行读写操作(

You're looking for the r+ or a+ mode, which allows read and write operations to files (see more).

使用r+时，该位置最初位于开头，但是读取一次会将其推向末尾，从而允许您追加.使用a+，该位置最初位于末尾.

With r+, the position is initially at the beginning, but reading it once will push it towards the end, allowing you to append. With a+, the position is initially at the end.

with open("filename", "r+") as f:
    # here, position is initially at the beginning
    text = f.read()
    # after reading, the position is pushed toward the end

    f.write("stuff to append")

with open("filename", "a+") as f:
    # here, position is already at the end
    f.write("stuff to append")

如果需要重新读取整个内容，则可以通过执行f.seek(0)返回到起始位置.

If you ever need to do an entire reread, you could return to the starting position by doing f.seek(0).

with open("filename", "r+") as f:
    text = f.read()
    f.write("stuff to append")

    f.seek(0)  # return to the top of the file
    text = f.read()

    assert text.endswith("stuff to append")

这篇关于如何在一个变量中同时在python中以读取和追加模式打开文件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！