86 – File modes

There are 16 different file modes. The four base modes are

1. r for reading;

2. w for writing;

3. a for appending; and

4. x for exclusive creation and writing.

The mode x is like w, but fails if the file already exists. In other words, it ensures you’re creating a new file.

The table below encodes the properties of each mode:

Mode	r	w	a	x
allows read	x
allows write		x	x	x
must exist	x
must not exist				x
positioned at start	x	x		x
positioned at end			x
always writes to end			x

These four base modes operate on files in text mode, by default, which is the same as appending a t to each mode. For example, the modes r and rt are the same. Instead, you can append a b to open the files in binary mode.

Finally, you can also append a + to any mode to enable writing and reading at the same time, although this is uncommon because it can be quite confusing.

Further reading:

• File modes in Python.