Creating processes: subprocess.Popen

What happens when you apply subprocess.run on a Linux command that starts a process that requires user input to terminate?

A simple example of such a program is xclock. It opens a new window displaying a clock until the window is closed by the user.

As the command subprocess.run creates a CompletedProcess object, the following Python script:

import subprocess as sp
res=sp.run(['xclock'])

starts a process and waits until it ends, that is, until somebody closes the window with the clock; see Figure 17.9:

Figure 17.9: The xclock window

This makes a difference to subprocess.Popen. It creates a _Popen object. The process itself becomes a Python object. It need not be completed to become an accessible Python object:

import subprocess as sp
p=sp.Popen(['xclock'])

The process is completed by either a user action on the clock window or by explicitly terminating the process with:

p.terminate()

With Popen, we can construct Linux pipes in Python...