医生说,
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,在模式后追加'b'以二进制模式打开文件;在没有这种区别的系统中,添加“b”没有任何效果。
这里
w+:打开文件进行读写操作。如果文件存在,则覆盖现有文件。如果该文件不存在,则创建一个新文件进行读写。
但是,如何用w+读取打开的文件?
医生说,
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,在模式后追加'b'以二进制模式打开文件;在没有这种区别的系统中,添加“b”没有任何效果。
这里
w+:打开文件进行读写操作。如果文件存在,则覆盖现有文件。如果该文件不存在,则创建一个新文件进行读写。
但是,如何用w+读取打开的文件?
当前回答
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.
其他回答
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。
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。
R代表读
W代表写
如果文件存在,R +为读写不删除原始内容,否则引发异常
W +表示删除原始内容,如果文件存在则读写,否则创建文件
例如,
>>> with open("file1.txt", "w") as f:
... f.write("ab\n")
...
>>> with open("file1.txt", "w+") as f:
... f.write("c")
...
$ cat file1.txt
c$
>>> with open("file2.txt", "r+") as f:
... f.write("ab\n")
...
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IOError: [Errno 2] No such file or directory: 'file2.txt'
>>> with open("file2.txt", "w") as f:
... f.write("ab\n")
...
>>> with open("file2.txt", "r+") as f:
... f.write("c")
...
$ cat file2.txt
cb
$
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。
Python中的所有文件模式
r for reading r+ opens for reading and writing (cannot truncate a file) w for writing w+ for writing and reading (can truncate a file) rb for reading a binary file. The file pointer is placed at the beginning of the file. rb+ reading or writing a binary file wb+ writing a binary file a+ opens for appending ab+ Opens a file for both appending and reading in binary. The file pointer is at the end of the file if the file exists. The file opens in the append mode. x open for exclusive creation, failing if the file already exists (Python 3)