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 wrote earlier...
    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'

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.

 

------------------------------------------------------------------------------------------------------------

 

Actually, there's something wrong about all the other answers about r+ mode.

test.in file's content

hello1
ok2
byebye3

And the py script's :

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

Execute it and the test.in's content will be changed to :

hello1
ok2
byebye3
addition

However, when we modify the script to :

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

the test.in also do the respond:

additionk2
byebye3

So, the r+ mode will allow us to cover the content from the beginning if we did't do the read operation. And if we do some read operation, f.write()will just append to the file.

By the way, if we f.seek(0,0) before f.write(write_content), the write_content will cover them from the positon(0,0).

 

Here is a list of the different modes of opening a file:

  • 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.

 


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