I know there are similar questions posted already, but non of the methods I have seen seems to work. I want to launch the application xfoil, on mac, with python subprocess, and send xfoil a bunch of commands with a script (xfoil is an application that runs in a terminal window and you interact with it through text commands). I am able to launch xfoil with the script, but I can't seem to find out how to send commands to it. This is the code I am currently trying:
import subprocess as sp
xfoil = sp.Popen(['open', '-a', '/Applications/Xfoil.app/Contents/MacOS/Xfoil'], stdin=sp.PIPE, stdout=sp.PIPE)
stdout_data = xfoil.communicate(input='NACA 0012')
I have also tried
xfoil.stdin.write('NACA 0012\n')
in order to send commands to xfoil.
As the man page says,
The open command opens a file (or a directory or URL), just as if you had double-clicked the file's icon.
Ultimately, the application gets started by LaunchServices, but that's not important—what's important is that it's not a child of your shell, or Python script.
Also, the whole point of open is to open the app itself, so you don't have to dig into it and find the Unix executable file. If you already have that, and want to run it as a Unix executable… just run it:
xfoil = sp.Popen(['/Applications/Xfoil.app/Contents/MacOS/Xfoil'], stdin=sp.PIPE, stdout=sp.PIPE)
As it turns out, in this case, MacOS/Xfoil isn't even the right program; it's apparently some kind of wrapper around Resources/xfoil, which is the actual equivalent to what you get as /usr/local/bin/xfoil on linux. So you want to do this:
xfoil = sp.Popen(['/Applications/Xfoil.app/Contents/Resouces/xfoil'], stdin=sp.PIPE, stdout=sp.PIPE)
(Also, technically, your command line shouldn't even work at all; the -a specifies an application, not a Unix executable, and you're supposed to pass at least one file to open. But because LaunchServices can launch Unix executables as if they were applications, and open doesn't check that the arguments are valid, open -a /Applications/Xfoil.app/Contents/MacOS/Xfoil ends up doing effectively the same thing as open /Applications/Xfoil.app/Contents/MacOS/Xfoil.)
For the benefit of future readers, I'll include this information from the comments:
If you just write a line to stdin and then return from the function/fall off the end of the main script/etc., the Popen object will get garbage collected, closing both of its pipes. If xfoil hasn't finished running yet, it will get an error the next time it tries to write any output, and apparently it handles this by printing Fortran runtime error: end of file (to stderr?) and bailing. You need to call xfoil.wait() (or something else that implicitly waits) to prevent this from happening.
Related
This script loops to open the temp.rtf file. Script pauses automatically until current file instance is closed. I get anywhere from 0 to 30 seconds delay before it opens a new window. I also noticed it when using cmd with subprocess.run in python. Can someone explain what is happening? This completely breaks python..
import sys, subprocess
def redir(tag):
if str(tag)=='journal':
subprocess.run("temp.rtf", shell=True)
while __name__=="__main__":
redir('journal')
Argument for redir (last line) is actually argv but this should work the same.
if __name__=="__main__":
while True:
redir('journal')
^gives same delay
*Using windows 10, task manager says 7% CPU max, nothing else.
Entering code into cmd gives no delay in opening the file but the same major delay is apparent in the cmd windows not closing for random amounts of time.
From your shell, type in the command to open the same file.
Run this simple test 6 times: which are the startup delay of every run?
You don't specify nor the operating system neither the application and the system load (other runnimg processes, cpu load, memory load).
The last comment by the author is significant:
Cmd.exe /C command- line
Every time a new command processor is started, it executes, before the command-line, other programs (auto startup entries).
You can use the switch /D before /C
/D Ignore registry AutoRun commands
Ref.
https://ss64.com/nt/cmd.html
To see the autoruns entries you can use Autoruns from sysinternals:
https://learn.microsoft.com/en-us/sysinternals/downloads/autoruns
If this switch doesn't work, I suggest you to see the other free tools at sysinternals, they can help you to find suspects and bottlenecks.
For example, process explorer:
https://learn.microsoft.com/en-us/sysinternals/downloads/process-explorer
I read How do you create a daemon in Python? and also this topic, and tried to write a very simple daemon :
import daemon
import time
with daemon.DaemonContext():
while True:
with open('a.txt', 'a') as f:
f.write('Hi')
time.sleep(2)
Doing python script.py works and returns immediately to terminal (that's the expected behaviour). But a.txt is never written and I don't get any error message. What's wrong with this simple daemon?
daemon.DaemonContext() has option working_directory that has default fault value / i.e. your program probably doesn't have permission to create a new file there.
The problem described here is solved by J.J. Hakala's answer.
Two additional (important) things :
Sander's code (mentioned here) is better than python-daemon. It is more reliable. Just one example: try to start two times the same daemon with python-daemon : big ugly error. With Sander's code : a nice notice "Daemon already running."
For those who want to use python-daemon anyway: DaemonContext() only makes a daemon. DaemonRunner() makes a daemon + control tool, allowing to do python script.py start or stop, etc.
One thing that's wrong with it, is it has no way to tell you what's wrong with it :-)
A daemon process is, by definition, detached from the parent process and from any controlling terminal. So if it's got something to say – such as error messages – it will need to arrange that before becoming a daemon.
From the python-daemon FAQ document:
Why does the output stop after opening the daemon context?
The specified behaviour in PEP 3143_ includes the requirement to
detach the process from the controlling terminal (to allow the process
to continue to run as a daemon), and to close all file descriptors not
known to be safe once detached (to ensure any files that continue to
be used are under the control of the daemon process).
If you want the process to generate output via the system streams
‘sys.stdout’ and ‘sys.stderr’, set the ‘DaemonContext’'s ‘stdout’
and/or ‘stderr’ options to a file-like object (e.g. the ‘stream’
attribute of a ‘logging.Handler’ instance). If these objects have file
descriptors, they will be preserved when the daemon context opens.
Set up a working channel of communication, such as a log file. Ensure the files you open aren't closed along with everything else, using the files_preserve option. Then log any errors to that channel.
I was trying to make a program in Python that would use os.system to open a file in Safari. In this case, I was trying to have it open a text copy of itself. The files name is foo.py.
import os, socket
os.system("python -m SimpleHTTPServer 4000")
IP = socket.gethostbyname(socket.gethostname())
osCommand = "open -a safari http://"+IP+":4000/foo.py"
os.system(osCommand)
system runs a program, then waits for it to finish, before returning.
So it won't get to the next line of your code until the server has finished serving. Which will never happen. (Well, you can hit ^C, and then it will stop serving—but then when you get to the next line that opens safari, it'll have no server to connect to anymore.)
This is one of the many reasons the docs for system basically tell you not to use it:
The subprocess module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using this function. See the Replacing Older Functions with the subprocess Module section in the subprocess documentation for some helpful recipes.
For example:
import subprocess, socket
server = subprocess.Popen(['python', '-m', 'SimpleHTTPServer', '4000'])
IP = socket.gethostbyname(socket.gethostname())
safari = subprocess.Popen(['open', '-a', 'safari', 'http://'+IP+':4000/foo.py'])
server.wait()
safari.wait()
That will start both programs in the background, and then wait for both to finish, instead of starting one, waiting for it to finish, starting the other, and waiting for it to finish.
All that being said, this is kind of a silly way to do what you want. What's wrong with just opening a file URL (like 'file:///{}'.format(os.path.abspath(sys.argv[0]))) in Safari? Or in the default web browser (which would presumably be Safari for you, but would also work on other platform, and for Mac users who used Chrome or Firefox, and so on) by using webbrowser.open on that URL?
My python script needs to be killed every hour and after I need to restarted it. I need this to do because it's possible sometimes (I create screenshots) a browser window is hanging because of a user login popup or something.. Anyway. I created 2 files 'reload.py' and 'screenshot.py'. I run reload.py by cronjob.
I thought something like this would work
# kill process if still running
try :
os.system("killall -9 screenshotTaker");
except :
print 'nothing to kill'
# reload or start process
os.execl("/path/to/script/screenshots.py", "screenshotTaker")
The problem is, and what I read aswel the second argument of execl (the given process name) doesn't work? How can I set a process name for it to make the kill do it's work?
Thanks in advance!
The first argument to os.execl is the path to the executable. The remaining arguments are passed to that executable as if their where typed on the command-line.
If you want "screenshotTaker" become the name of the process, that is "screenshots.py" responsibility to do so. Do you do something special in that sense in that script?
BTW, a more common approach is to keep track (in /var/run/ usually) of the PID of the running program. And kill it by PID. This could be done with Python (using os.kill) At system-level, some distribution have helpers for that exact purpose. For example, on Debian there is start-stop-daemon. Here is a excerpt of the man:
start-stop-daemon(8) dpkg utilities start-stop-daemon(8)
NAME
start-stop-daemon - start and stop system daemon programs
SYNOPSIS
start-stop-daemon [options] command
DESCRIPTION
start-stop-daemon is used to control the creation and termination of
system-level processes. Using one of the matching options,
start-stop-daemon can be configured to find existing instances of a
running process.
I am writing a Python program which runs a virtual terminal. Currently I am launching it like so:
import pexpect, thread
def create_input(child, scrollers, textlength=80, height=12):
while 1:
newtext = child.readline()
print newtext
child = pexpect.spawn("bash", timeout=30000)
thread.start_new_thread(create_input,(child))
This works, and I can send commands to it via child.send(command). However, I only get entire lines as output. This means that if I launch something like Nano or Links, I don't receive any output until the process has completed. I also can't see what I'm typing until I press enter. Is there any way to read the individual characters as bash outputs them?
You would need to change the output of whatever program bash is running to be unbuffered instead of line buffering. A good amount of programs have a command line option for unbuffered output.
The expect project has a tool called unbuffer that looks like it can give you all bash output unbuffered. I have personally never used it, but there are other answers here on SO that also recommend it: bash: force exec'd process to have unbuffered stdout
The problem is lies in something else. If you open an interactive shell normally a terminal window is opened that runs bash, sh, csh or whatever. See the word terminal!
In the old days, we connected a terminal to a serial port (telnet does the same but over ip), again the word terminal.
Even a dumb terminal respond to ESC codes, to report its type and to set the cursor position, colors, clear screen etc.
So you are starting a subprocess with interactive output, but there is no way in telling that shell and subprocesses are to a terminal in this setup other than with bash startup parameters if there are any.
I suggest you enable telnetd but only on localhost (127.0.0.1)
Within your program, make a socket and connect to localhost:telnet and look up how to emulate a proper terminal. If a program is in line mode you are fine but if you go to full screen editing, somewhere you will need an array of 80x24 or 132x24 or whatever size you want to store its characters, color. You also need to be able to shift lines up in that array.
I have not looked but I cannot imagine there is no telnet client example in python, and a terminal emu must be there too!
Another great thing is that telnet sessions clean up if the the ip connection is lost, eliminating ghost processes.
Martijn