I am running a script that launches a program via cmd and then, while the program is open, checks the log file of the program for errors. If any, close the program.
I cannot use taskkill command since I don't know the PID of the process and the image is the same as other processes that I don't want to kill.
Here is a code example:
import os, multiprocessing, time
def runprocess():
os.system('"notepad.exe"')
if __name__ == '__main__':
process = multiprocessing.Process(target=runprocess,args=[])
process.start()
time.sleep(5)
#Continuously checking if errors in log file here...
process_has_errors = True #We suppose an error has been found for our case.
if process_has_errors:
process.terminate()
The problem is that I want the notepad windows to close. It seems like the terminate() method will simply disconnect the process without closing all it's tasks.
What can I do to make sure to end all pending tasks in a process when terminating it, instead of simply disconnecting the process from those tasks?
You can use taskkill but you have to use the /T (and maybe /F) switch so all child processes of the cmd process are killed too. You get the process id of the cmd task via process.pid.
You could use a system call if you know the name of the process:
import os
...
if process_has_errors:
processName = "notepad.exe"
process.terminate()
os.system(f"TASKKILL /F /IM {processName}")
I'm trying to port a shell script to the much more readable python version. The original shell script starts several processes (utilities, monitors, etc.) in the background with "&". How can I achieve the same effect in python? I'd like these processes not to die when the python scripts complete. I am sure it's related to the concept of a daemon somehow, but I couldn't find how to do this easily.
While jkp's solution works, the newer way of doing things (and the way the documentation recommends) is to use the subprocess module. For simple commands its equivalent, but it offers more options if you want to do something complicated.
Example for your case:
import subprocess
subprocess.Popen(["rm","-r","some.file"])
This will run rm -r some.file in the background. Note that calling .communicate() on the object returned from Popen will block until it completes, so don't do that if you want it to run in the background:
import subprocess
ls_output=subprocess.Popen(["sleep", "30"])
ls_output.communicate() # Will block for 30 seconds
See the documentation here.
Also, a point of clarification: "Background" as you use it here is purely a shell concept; technically, what you mean is that you want to spawn a process without blocking while you wait for it to complete. However, I've used "background" here to refer to shell-background-like behavior.
Note: This answer is less current than it was when posted in 2009. Using the subprocess module shown in other answers is now recommended in the docs
(Note that the subprocess module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using these functions.)
If you want your process to start in the background you can either use system() and call it in the same way your shell script did, or you can spawn it:
import os
os.spawnl(os.P_DETACH, 'some_long_running_command')
(or, alternatively, you may try the less portable os.P_NOWAIT flag).
See the documentation here.
You probably want the answer to "How to call an external command in Python".
The simplest approach is to use the os.system function, e.g.:
import os
os.system("some_command &")
Basically, whatever you pass to the system function will be executed the same as if you'd passed it to the shell in a script.
I found this here:
On windows (win xp), the parent process will not finish until the longtask.py has finished its work. It is not what you want in CGI-script. The problem is not specific to Python, in PHP community the problems are the same.
The solution is to pass DETACHED_PROCESS Process Creation Flag to the underlying CreateProcess function in win API. If you happen to have installed pywin32 you can import the flag from the win32process module, otherwise you should define it yourself:
DETACHED_PROCESS = 0x00000008
pid = subprocess.Popen([sys.executable, "longtask.py"],
creationflags=DETACHED_PROCESS).pid
Use subprocess.Popen() with the close_fds=True parameter, which will allow the spawned subprocess to be detached from the Python process itself and continue running even after Python exits.
https://gist.github.com/yinjimmy/d6ad0742d03d54518e9f
import os, time, sys, subprocess
if len(sys.argv) == 2:
time.sleep(5)
print 'track end'
if sys.platform == 'darwin':
subprocess.Popen(['say', 'hello'])
else:
print 'main begin'
subprocess.Popen(['python', os.path.realpath(__file__), '0'], close_fds=True)
print 'main end'
Both capture output and run on background with threading
As mentioned on this answer, if you capture the output with stdout= and then try to read(), then the process blocks.
However, there are cases where you need this. For example, I wanted to launch two processes that talk over a port between them, and save their stdout to a log file and stdout.
The threading module allows us to do that.
First, have a look at how to do the output redirection part alone in this question: Python Popen: Write to stdout AND log file simultaneously
Then:
main.py
#!/usr/bin/env python3
import os
import subprocess
import sys
import threading
def output_reader(proc, file):
while True:
byte = proc.stdout.read(1)
if byte:
sys.stdout.buffer.write(byte)
sys.stdout.flush()
file.buffer.write(byte)
else:
break
with subprocess.Popen(['./sleep.py', '0'], stdout=subprocess.PIPE, stderr=subprocess.PIPE) as proc1, \
subprocess.Popen(['./sleep.py', '10'], stdout=subprocess.PIPE, stderr=subprocess.PIPE) as proc2, \
open('log1.log', 'w') as file1, \
open('log2.log', 'w') as file2:
t1 = threading.Thread(target=output_reader, args=(proc1, file1))
t2 = threading.Thread(target=output_reader, args=(proc2, file2))
t1.start()
t2.start()
t1.join()
t2.join()
sleep.py
#!/usr/bin/env python3
import sys
import time
for i in range(4):
print(i + int(sys.argv[1]))
sys.stdout.flush()
time.sleep(0.5)
After running:
./main.py
stdout get updated every 0.5 seconds for every two lines to contain:
0
10
1
11
2
12
3
13
and each log file contains the respective log for a given process.
Inspired by: https://eli.thegreenplace.net/2017/interacting-with-a-long-running-child-process-in-python/
Tested on Ubuntu 18.04, Python 3.6.7.
You probably want to start investigating the os module for forking different threads (by opening an interactive session and issuing help(os)). The relevant functions are fork and any of the exec ones. To give you an idea on how to start, put something like this in a function that performs the fork (the function needs to take a list or tuple 'args' as an argument that contains the program's name and its parameters; you may also want to define stdin, out and err for the new thread):
try:
pid = os.fork()
except OSError, e:
## some debug output
sys.exit(1)
if pid == 0:
## eventually use os.putenv(..) to set environment variables
## os.execv strips of args[0] for the arguments
os.execv(args[0], args)
You can use
import os
pid = os.fork()
if pid == 0:
Continue to other code ...
This will make the python process run in background.
I haven't tried this yet but using .pyw files instead of .py files should help. pyw files dosen't have a console so in theory it should not appear and work like a background process.
I am trying to make a little script in python to stream from a gopro to PC
from selenium import webdriver
from subprocess import call
import subprocess, sys
import time
import urllib
import urllib2
pid = subprocess.Popen([sys.executable, "Sel.py"])
call(["ffplay", "-fflags", "nobuffer", "udp://:8554"])
driver = webdriver.Firefox(executable_path='/usr/bin/geckodriver')
while True:
time.sleep(10)
driver.get("http://10.5.5.9/gp/gpControl/execute?p1=gpStream&a1=proto_v2&c1=restart")
I am not really familiar with python and my objective is to open ffplay
with those options and then execute the remaining part of the program (reloading a page every 10 seconds).
Now when i run the script it continuously make that system call.
Is there a way to detach the execution of ffplay from the execution of the python code?
Don't repeatedly call the stream http command, use a keep alive magic command instead: http://github.com/konradit/goprostream
'Call' will always wait for the process it is calling to complete. I think you need to use Popen for both operations as it will return control to your code. There is a short tutorial at https://pythonspot.com/python-subprocess/
I need to call a bash Script Out of my Python Script.
import subprocess
subprocess.call("path/to/script.sh")
This is working, but the Script is starting another programm and therefore wont Exit. So my main Loop is blocked by the subprocess.
Is there a way to call the Script as Thread, not subprocess in Python?
You're better off using Popen
Execute a child program in a new process. On Unix, the class uses
os.execvp()-like behavior to execute the child program. On Windows,
the class uses the Windows CreateProcess() function. The arguments to
Popen are as follows
But if you insist on using threads this might also work:
import subprocess
import threading
def basher():
subprocess.call("echo hello > /tmp/test.txt", shell=True)
t = threading.Thread(target=basher)
t.start()
print('started')
# doing something else
t.join()
print('finished')
Don't use call; its only purpose is to block until the command exits. Use Popen directly:
import subprocess
p = subprocess.Popen("path/to/script.sh")
Now script.sh runs in the forked process while your Python script continues. Use p.wait() when you are ready to check if the script has completed.
Since you specifically asked for a separate thread, I recommend using the multiprocessing module (documentation):
from multiprocessing import Process
import subprocess
def myTask():
subprocess.call("path/to/script.sh")
p = Process(target=myTask) # creates a new thread which will run the function myTask
p.start() # starts the thread
# the script is now running in a separate thread
# you can now continue doing what you want
If at some point in your python script (e.g. before exiting) you want to make sure that the bash script has finished running you can call p.join() which blocks the python script until the bash script has terminated.
Under Linux Ubuntu operating system, I run the test.py scrip which contain a GObject loop using subprocess by:
subprocess.call(["test.py"])
Now, this test.py will creat process. Is there a way to kill this process in Python?
Note: I don't know the process ID.
I am sorry if I didn't explain my problem very clearly as I am new to this forms and new to python in general.
I would suggest not to use subprocess.call but construct a Popen object and use its API: http://docs.python.org/2/library/subprocess.html#popen-objects
In particular:
http://docs.python.org/2/library/subprocess.html#subprocess.Popen.terminate
HTH!
subprocess.call() is just subprocess.Popen().wait():
from subprocess import Popen
from threading import Timer
p = Popen(["command", "arg1"])
print(p.pid) # you can save pid to a file to use it outside Python
# do something else..
# now ask the command to exit
p.terminate()
terminator = Timer(5, p.kill) # give it 5 seconds to exit; then kill it
terminator.start()
p.wait()
terminator.cancel() # the child process exited, cancel the hit
subprocess.call waits for the process to be completed and returns the exit code (integer) value , hence there is no way of knowing the process id of the child process. YOu should consider using subprocess.Popen which forks() child process.