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

By mkyong | Updated: May 22, 2021

Viewed: 61,843 (+160 pv/w)

Tags: append file file mode python python io read file write file

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

Table of contents

• 1. Difference between r, r+, w, w+, a and a+
• 2. What is + means in open()?
• 3. Difference between r and r+ in open()
  • 3.1 Read a file with r
  • 3.2 Read and write a file with r+
• 4. Difference between w and w+ in open()
  • 4.1 Write a file with w
  • 4.2 Read and write a file with w+
• 5. Difference between a and a+ in open()
  • 5.1 Append a file with a
  • 5.2 Append a file with a+
• 6. Difference between r+ and w+ in open()
• 7. Difference between r+ and a+ in open()
• 8. Difference between w+ and a+ in open()
• 9. Download Source Code
• 10. References

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.

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.

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

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

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

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

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

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.

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

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

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

10. References

• Python doc – open
• fopen() file modes
• How to write a file in Python
• How to append a file in Python
• How to read a file in Python