知识问答

如何打开文件进行读写？

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问题：如何打开文件进行读写？
回答 0
回答 1
回答 2
回答 3

问题：如何打开文件进行读写？

有没有办法打开文件进行读写？

解决方法是，打开文件进行写入，将其关闭，然后再次打开以进行读取。但是，有没有办法打开一个文件都阅读和写作？

点击查看英文原文

Is there a way to open a file for both reading and writing?

As a workaround, I open the file for writing, close it, then open it again for reading. But is there a way to open a file for both reading and writing?

回答 0

在不关闭和重新打开的情况下，读取文件然后写入文件（覆盖所有现有数据）的方法如下：

with open(filename, "r+") as f:
    data = f.read()
    f.seek(0)
    f.write(output)
    f.truncate()
点击查看英文原文

Here’s how you read a file, and then write to it (overwriting any existing data), without closing and reopening:

with open(filename, "r+") as f:
    data = f.read()
    f.seek(0)
    f.write(output)
    f.truncate()

回答 1

r+是同时读取和写入的规范模式。这与使用fopen()系统调用没有什么不同，因为file()/ open()只是围绕此操作系统调用的一个小包装。

点击查看英文原文

r+ is the canonical mode for reading and writing at the same time. This is not different from using the fopen() system call since file() / open() is just a tiny wrapper around this operating system call.

回答 2

总结I / O行为

|          Mode          |  r   |  r+  |  w   |  w+  |  a   |  a+  |
| :--------------------: | :--: | :--: | :--: | :--: | :--: | :--: |
|          Read          |  +   |  +   |      |  +   |      |  +   |
|         Write          |      |  +   |  +   |  +   |  +   |  +   |
|         Create         |      |      |  +   |  +   |  +   |  +   |
|         Cover          |      |      |  +   |  +   |      |      |
| Point in the beginning |  +   |  +   |  +   |  +   |      |      |
|    Point in the end    |      |      |      |      |  +   |  +   |

和决策分支

点击查看英文原文

Summarize the I/O behaviors

|          Mode          |  r   |  r+  |  w   |  w+  |  a   |  a+  |
| :--------------------: | :--: | :--: | :--: | :--: | :--: | :--: |
|          Read          |  +   |  +   |      |  +   |      |  +   |
|         Write          |      |  +   |  +   |  +   |  +   |  +   |
|         Create         |      |      |  +   |  +   |  +   |  +   |
|         Cover          |      |      |  +   |  +   |      |      |
| Point in the beginning |  +   |  +   |  +   |  +   |      |      |
|    Point in the end    |      |      |      |      |  +   |  +   |

and the decision branch

回答 3

我已经尝试过类似的方法，并且可以按预期工作：

f = open("c:\\log.log", 'r+b')
f.write("\x5F\x9D\x3E")
f.read(100)
f.close()

哪里：

f.read（size）-要读取文件的内容，请调用f.read（size），它将读取一定数量的数据并将其作为字符串返回。

和：

f.write（string）将string的内容写入文件，返回None。

另外，如果您打开有关读写文件的Python教程，则会发现：

“ r +”打开文件以供读取和写入。

在Windows上，附加到模式的’b’以二进制模式打开文件，因此也有’rb’，’wb’和’r + b’之类的模式。

点击查看英文原文

I have tried something like this and it works as expected:

f = open("c:\\log.log", 'r+b')
f.write("\x5F\x9D\x3E")
f.read(100)
f.close()

Where:

f.read(size) – To read a file’s contents, call f.read(size), which reads some quantity of data and returns it as a string.

And:

f.write(string) writes the contents of string to the file, returning None.

Also if you open Python tutorial about reading and writing files you will find that:

‘r+’ opens the file for both reading and writing.

On Windows, ‘b’ appended to the mode opens the file in binary mode, so there are also modes like ‘rb’, ‘wb’, and ‘r+b’.