What does python3 open “x” mode do?

Question

What does the new open file mode \"x\" do in python 3?

here is the doc of python 3:

\'r\': open for reading (default)

\'w\': open

Answer 1

Yes, that's basically it. It calls the underlying operating system code with the two flags O_CREAT and O_EXCL, which attempts to open the file exclusively, creating a new one if it doesn't currently exist.

It's handy if you may find two instances of your program running concurrently, the use of x mode will ensure only one will successfully create a file, with the other one failing.

A classic example is daemons that write their process ID into a pid file (so that can be easily signalled later on). By using x, you can guarantee that only one daemon can be running at a time, something that's harder to do without the x mode, and prone to race conditions.