Python difference between r+, w+ and a+ in open()

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This article shows the difference between r, r+, w, w+, a and a+ in Python open() function.

Table of contents

P.S Tested with Python 3.8

1. Difference between r, r+, w, w+, a and a+

1.1 Read below table for the difference between open modes r, r+, w, w+, a and a+ in open() function.

r r+ w w+ a a+
read * * * *
write * * * * *
create * * * *
truncate * *
position at start * * * *
position at end * *

P.S In this context, truncate means delete the content of the file.

1.2 Definition of open modes r, r+, w, w, a, a+:

  • The r throws an error if the file does not exist or opens an existing file without truncating it for reading; the file pointer position at the beginning of the file.
  • The r+ throws an error if the file does not exist or opens an existing file without truncating it for reading and writing; the file pointer position at the beginning of the file.
  • The w creates a new file or truncates an existing file, then opens it for writing; the file pointer position at the beginning of the file.
  • The w+ creates a new file or truncates an existing file, then opens it for reading and writing; the file pointer position at the beginning of the file.
  • The a creates a new file or opens an existing file for writing; the file pointer position at the end of the file.
  • The a+ creates a new file or opens an existing file for reading and writing, and the file pointer position at the end of the file.

2. What is + means in open()?

The + adds either reading or writing to an existing open mode, aka update mode.

  • The r means reading file; r+ means reading and writing the file.
  • The w means writing file; w+ means reading and writing the file.
  • The a means writing file, append mode; a+ means reading and writing file, append mode.

3. Difference between r and r+ in open()

The r+ adds writing file to the existing r mode.

A text file for testing.

file.txt

welcome to python 1
welcome to python 2
welcome to python 3
welcome to python 4

3.1 Read a file with r


with open('file.txt') as f:  # default `r` mode
    print(f.read())

Output

Terminal

welcome to python 1
welcome to python 2
welcome to python 3
welcome to python 4

In r mode, if we write the file, Python throws io.UnsupportedOperation: not writable


with open('file.txt', 'r') as f:  # default `r` mode
    f.write("test \n")            # throws UnsupportedOperation

3.2 Read and write a file with r+

In r+ mode, we can read and write the file, but the file pointer position is at the beginning of the file; if we write the file directly, it will overwrite the beginning content.

See the below example:


with open('file.txt', 'r+') as f:
    f.write("new line \n")

Output

Terminal

new line
python 1
welcome to python 2
welcome to python 3
welcome to python 4

The below example uses f.read() to move the file pointer to the end of the file, and append a new line.


# alternative, open with `a` mode
with open('file.txt', 'r+') as f:
    f.read()                # move file position to the end of the file.
    f.write("new line \n")

Output

Terminal

welcome to python 1
welcome to python 2
welcome to python 3
welcome to python 4
new line

Please comment below if you know other r+ examples, thanks.

4. Difference between w and w+ in open()

The w+ adds reading file to the existing w mode.

4.1 Write a file with w


with open('file.txt', 'w+') as f:   # create a new file or truncates it
    f.write("test 1\n")
    f.write("test 2\n")
    f.write("test 3\n")

Output

file.txt

test 1
test 2
test 3

4.2 Read and write a file with w+


with open('file.txt', 'w+') as f:   # create a new file or truncates it
    f.write("test 1\n")
    f.write("test 2\n")
    f.write("test 3\n")             # now the file pointer is at the end
    f.seek(0)                       # move the file pointer to the beginning
    lines = f.read()                # read it, now we can read!
    print(lines)                    # print it

Output

Terminal

test 1
test 2
test 3

5. Difference between a and a+ in open()

The a+ adds reading file to the existing a mode.

A text file for testing.

file.txt

welcome to python 1
welcome to python 2
welcome to python 3
welcome to python 4

5.1 Append a file with a


with open('file.txt', 'a') as f:
    f.write("4")

Output

file.txt

welcome to python 1
welcome to python 2
welcome to python 3
welcome to python 4
4

5.2 Append a file with a+

  1. Open a file for reading and writing with a+.
  2. Counts the number of the lines.
  3. Append the result to the file.

with open('file.txt', 'a+') as f:
    f.seek(0)                       # file pointer at end, move to beginning
    lines = f.readlines()           # read all and file pointer at end again
    f.write("\n" + str(len(lines))) # append number of lines to a file

Output

file.txt

welcome to python 1
welcome to python 2
welcome to python 3
welcome to python 4
4

6. Difference between r+ and w+ in open()

Below is the difference between r+ and w+:

  1. If the file does not exist, r+ throws FileNotFoundError; the w+ creates the file.
  2. If the file exists, r+ opens it without truncating; the w+ truncates the file and opens it.

7. Difference between r+ and a+ in open()

Below is the difference between r+ and a+:

  1. If the file does not exist, r+ throws FileNotFoundError; the a+ creates the file.
  2. For r+ mode, the initial file pointer position at the beginning of the file; For a+ mode, the initial file pointer position at the end of the file.

8. Difference between w+ and a+ in open()

Below is the difference between w+ and a+:

  1. If the file exists, w+ truncates the file and opens it; a+ opens it without truncating.
  2. For w+ mode, the initial file pointer position at the beginning of the file; For a+ mode, the initial file pointer position at the end of the file.

9. Download Source Code

$ git clone https://github.com/mkyong/python

$ cd io

10. References

mkyong

Founder of Mkyong.com, passionate Java and open-source technologies. If you enjoy my tutorials, consider making a donation to these charities.

4 Comments
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tom
4 years ago

4.1 Write a file with w
with open(‘file.txt’, ‘w+’) as f: # create a new file or truncates it

you’ve made a small mistake there. it won’t be w+

3
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jessie
3 years ago

very helpful!

2
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Alejandro
3 years ago

Thanks so much

2
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Rohith
4 years ago

It was much useful. Thank u.

1
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