被python文件模式“w+"搞糊涂了； [英] Confused by python file mode "w+"

问题描述

来自 doc，

模式'r+'、'w+' 和'a+' 打开文件进行更新(注意'w+' 会截断文件).在区分二进制文件和文本文件的系统上，将b"附加到模式以二进制模式打开文件；在没有这种区别的系统上，添加b"无效.

Modes 'r+', 'w+' and 'a+' open the file for updating (note that 'w+' truncates the file). Append 'b' to the mode to open the file in binary mode, on systems that differentiate between binary and text files; on systems that don’t have this distinction, adding the 'b' has no effect.

和这里

w+ :打开一个文件进行读写.如果文件存在，则覆盖现有文件.如果文件不存在，则创建一个新文件进行读写.

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.

但是，如何读取用 w+ 打开的文件?

But, how to read a file open with w+?

推荐答案

假设您正在使用 with 语句打开文件，就像您应该的那样.然后你会做这样的事情来从你的文件中读取:

Let's say you're opening the file with a with statement like you should be. Then you'd do something like this to read from your file:

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
')
    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
'

请注意 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，并将返回一个空字符串.

Note the f.seek(0) -- if you forget this, the f.read() call will try to read from the end of the file, and will return an empty string.

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