ValueError: must have exactly one of create/read/write/append mode

ValueError: must have exactly one of create/read/write/append mode #

The Python "ValueError: must have exactly one of create/read/write/append mode" occurs when we specify an incorrect mode when opening a file. To solve the error, use the r+ mode if you need to open the file for both reading and writing.

valueerror must have exactly one of create read write append mode

Here is an example of how the error occurs.

main.py

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# 👇️ using incorrect 'rw' mode
# ⛔️ ValueError: must have exactly one of create/read/write/append mode
with open('example.txt', 'rw', encoding='utf-8') as my_file:
    read_data = my_file.read()
    print(read_data)

    my_file.write('first line' + '\n')
    my_file.write('second line' + '\n')
    my_file.write('third line' + '\n')

    my_file.seek(0)
    print(my_file.read())

We used an unsupported rw mode which caused the error.

If you need to open a file for both reading and writing, use the r+ mode instead.

main.py

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# ✅ using r+ mode
with open('example.txt', 'r+', encoding='utf-8') as my_file:
    read_data = my_file.read()
    print(read_data)

    my_file.write('first line' + '\n')
    my_file.write('second line' + '\n')
    my_file.write('third line' + '\n')

    my_file.seek(0)
    print(my_file.read())

The r+ mode opens the file for reading and writing and positions the stream at the beginning of the file.

You might also see the w+ mode being used. It opens the file for reading and writing and creates the file if it doesn't already exist.

If the file exists, it is truncated. Truncating the file means that all contents of the file are erased.

main.py

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with open('example-2.txt', 'w+', encoding='utf-8') as my_file:
    read_data = my_file.read()
    print(read_data)

    my_file.write('first line' + '\n')
    my_file.write('second line' + '\n')
    my_file.write('third line' + '\n')

    my_file.seek(0)
    print(my_file.read())

On the other hand, the r+ mode doesn't create the file if it doesn't exist, nor does it truncate the file.

Both the r+ and w+ modes position the stream at the beginning of the file.

There is also an a+ mode which opens the file for reading and writing.

The a+ mode creates the file if it doesn't already exist, but it positions the stream at the end of the file.

main.py

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with open('example-3.txt', 'a+', encoding='utf-8') as my_file:
    read_data = my_file.read()
    print(read_data)

    my_file.write('first line' + '\n')
    my_file.write('second line' + '\n')
    my_file.write('third line' + '\n')

    my_file.seek(0)
    print(my_file.read())

The difference between the a+ mode and the other 2 is that the stream is positioned at the end of the file.

The a+ mode also doesn't truncate the file if it already exists.

You can view all of the other possible modes to open a file in in this table of the official docs.

ValueError: must have exactly one of create/read/write/append mode

ValueError: must have exactly one of create/read/write/append mode #

Borislav Hadzhiev