[Python] How can I use /dev/ptmx for creating a virtual serial port?

I have a program, using PySerial, and I want to test it without using a real serial port device.

In Windows, I use com0com, and in Linux, I know there is a method to create a virtual serial port pair without using additional programs.

So I look up the manual, and found pts, /dev/ptmx, but I don't know how to create a pair by following the manual. What is some example?

I tried (in Python):

f = open("/dev/ptmx", "r")


And it works; /dev/pts/4 is created.

And I tried:

f = open("/dev/4", "w")


And the result is:

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
IOError: [Errno 5] Input/output error: '/dev/pts/4'


edit: I found a solution (workround), using socat.

socat PTY,link=COM8 PTY,link=COM9


Then COM8 and COM9 are created as a virtual serial port pair.

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