How to read stdout from subprocess as it is being produced

[Albert Hopkins]

On Fri, 2008-12-19 at 06:34 -0800, Alex wrote:
> Hi,
> 
> I have a Pyhon GUI application that launches subprocess.
> I would like to read the subprocess' stdout as it is being produced
> (show it in GUI), without hanging the GUI.
> 
> I guess threading will solve the no-hanging issue, but as far as I
> searched for now, I've only seen how to read the stdout after
> subprocess is finished.
> 

I believe that's going to be highly dependent upon the particular, yet
unspecified, GUI toolkit/API.

There are probably a few ways. You're toolkit might native support for
this, but one way would be to use a timer.  Here is some pseudocode:

class MyWindow(toolkit.Window):
    def __init__(self, ...):
        ...
        self.subprocess = subprocess.Popen(..., stdout=subprocess.PIPE)
	self.running = True

	...
        toolkit.set_timeout(TIMEOUT_VAL, self.read_stdout)

    def read_stdout(self, ...):
        if not self.running:
            return
        char = self.subprocess.stdout.read(1)
        if char == '':
            self.running = False
            return
        self.update_something(char)
        toolkit.set_timeout(TIMEOUT_VAL, self.read_stdout)