I'm doing a simple python gui and on button click it will run a simple command:
os.system("C:/cygwin64/bin/bash.exe")
When I look in the console it ran correctly and but my guy freezes and is not responding.
If I run the the command in the console without python it works perfectly and I start cygwin terminal.
If you know what is cygwin is there a better way to start it in the same terminal?
os.system blocks the current thread, you can use os.popen in order to do that in another thread, and it also gives you few methods to detach/read/write etc' that process.
for example,
import os
a = os.popen("python -c 'while True: print(1)'")
will create a new process that will be terminated as soon as you terminate your script.
you can do
for i in a:
print(i)
for example, and it will block the thread as os.system does.
you can a.detach() it whenever you want to terminate the process.
However, os.system
import os
os.system("python -c 'while True: print(1)'")
it will output the 1s forever until you terminate the script.
You can use function Popen in package subprocess. It has many possible arguments that allow you to pipe input to and/or pipe output from the program you are running. But if you just want to execute bash.exe while allowing your original Python program to continue running and eventually wait for the completion of bash.exe, then:
import subprocess
# pass a list of command-line arguments:
p = subprocess.Popen(["C:/cygwin64/bin/bash.exe"])
... # continue executing
# wait for the subprocess (bash.exe) to end:
exit_code = p.wait()
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.
After start.exe is executed by Python, the output of start.exe is displayed in the python stdout. However 5 seconds later, we do not see Quitting printed and the task is not killed.
Is there an easier way to terminate an exe that was originally started by Python? Like getting a handle for the exe executed and using that handle to kill the process.
import subprocess
import os
import time
subprocess.call(['.\\start.exe'])
time.sleep(5)
print("Quitting")
os.system("taskkill /im start.exe")
As you can see at the subprocess documentation, the call function blocks until the process completes.
I believe that you should use the Popen functions as it doesn't block, and provides you a process handle.
Then, you can kill it like this: p.kill(), where p is the result from the Popen function.
The reason is that subprocess.call will wait for your start.exe to complete before continuing your script.
You can get a popen object (with better functionality) to your process via:
import subprocess
import os
import time
process = subprocess.Popen(['.\\start.exe'])
time.sleep(5)
print("Quitting")
process.terminate()
I am starting a python script on one terminal and then from another terminal issuing a kill -9 to kill the process. I am hoping that even when the parent process is killed the thread will continue to execute and touch the file. But that is not happening. Any clue how I can achieve this?
import time,os
import threading
# Create your tests here.
def a(fname):
print "a"
time.sleep(20)
touch(fname)
def touch(fname, times=None):
with open(fname, 'a'):
os.utime(fname, times)
print "touched"
fname = "test.txt"
t = threading.Thread(target=a, args=(fname,))
t.setDaemon(True)
t.start()
t.join()
What you are trying is impossible, unfortunately. Threads can only run as long as their parent process runs. If you want to start executing some code from your script, but have that code continue executing after your script exits, you should move that code into a separate script and use the subprocess module to launch it. Specifically, you can use subprocess.Popen to launch the script without blocking to wait for it to complete:
subprocess.Popen(['./yourscript.py', '-a', 'opt'])
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.