File Opening Modes — r, w, a, r+, w+, a+, x, and x+

The mode tells Python whether you may read, write, append, or create the file, and what happens if that name already exists.

Use the playground at the bottom of this page, then take the quiz.

What you will learn

• The eight opening modes: r, w, a, r+, w+, a+, x, x+
• Which modes create a file and which modes require it to exist
• The difference between overwrite, append, and exclusive create
• Which exception appears when the mode and the file do not match

The idea

If you omit the mode, Python uses "r". Read modes fail with FileNotFoundError when the name is missing. The exception for an exclusive create that finds an existing file is FileExistsError.

Mode	File must exist?	Read	Write	If the file already exists
r	Yes	Yes	No	Leave it unchanged
w	No	No	Yes	Overwrite the old data
a	No	No	Yes	Append after the old data
r+	Yes	Yes	Yes	Keep data; pointer starts at the beginning
w+	No	Yes	Yes	Overwrite, then you may read
a+	No	Yes	Yes	Append; seek to the start before reading
x	No	No	Yes	FileExistsError if the name exists
x+	No	Yes	Yes	FileExistsError if the name exists

w and w+ are for a fresh copy of the file. a and a+ keep what is already there and add more. x and x+ create the name once. Use them when accidentally replacing a file would be a mistake.

After a w+ write, the pointer sits at the end. Call seek(0) before read() if you want the text you just stored. The same seek is required for a+.

Example

with open("notebook.txt", "w", encoding="utf-8") as handle:
    handle.write("Avery Lane\n")

with open("notebook.txt", "a", encoding="utf-8") as handle:
    handle.write("Jordan Hale\n")

with open("notebook.txt", "r", encoding="utf-8") as handle:
    print(handle.read())

The first write creates the file. The second open uses append, so the first line is still there. Change "a" to "w" in the playground and run again: the first line disappears because write mode overwrites.

Key takeaways

• "r" is the default and raises FileNotFoundError if the file is missing

• "w" overwrites; "a" appends

• + adds the other direction: read and write

• "x" creates a file only when the name is new

• The real exception name is FileExistsError

• Previous: Files and Streams

• Next: open() and with open()