Python newbie here. Sorry if I am a bit unclear.
I have a Python script that reads temperature, and I have another script that grabs the temperature value from the first one. If the first script terminates, the second will terminate with it.
How can I keep the second sript from terminating?
Thank you ;)
This isn't a direct answer to your question, but it's more of a directional consideration that you need to think about.
Since you're talking about temperature monitoring, it's a classic example for a Publish Subscribe model. Recently protocols like MQTT have gained in popularity, and is really helpful for the scenario that you're in.
You should really design your application with scalability in mind and explore before just using threaded python code. There's a cool python example here for MQTT.
Related
Okay, so basically I am creating a website. The data I need to display on this website is delivered twice daily, where I need to read the delivered data from a file and store this new data in the database (instead of the old data).
I have created the python functions to do this. However, I would like to know, what would be the best way to run this script, while my flask application is running? This may be a very simple answer, but I have seen some answers saying to incorporate the script into the website design (however these answers didn't explain how), and others saying to run it separately. The script needs to run automatically throughout the day with no monitoring or input from me.
TIA
Generally it's a really bad idea to put a webserver to handle such tasks, that is the flask application in your case. There are many reasons for it so just to name a few:
Python's Achilles heel - GIL.
Sharing system resources of the application between users and other operations.
Crashes - it happens, it could be unlikely but it does. And if you are not careful, the web application goes down along with it.
So with that in mind I'd advise you to ditch this idea and use crontabs. Basically write a script that does whatever transformations or operations it needs to do and create a cron job at a desired time.
I have a flow sensor that I have to read with c because python isn't fast enough but the rest of my code is python. What I want to do is have the c code running in the background and just have the python request a value from it every now and then. I know that popen is probably the easiest way to do this but I don't fully understand how to use it. I don't want completed code I just want a way to send text/numbers back and forth between a python and a c code. I am running raspbian on a raspberry pi zero w. Any help would be appreciated.
Probably not a full answer, but I expect it gives some hints and it is far too long for a comment. You should think twice about your requirements, because it will probably not be that easy depending on your proficiency in C and what OS you are using.
If I have correctly understood, you have a sensor that sends data (which is already weird unless the sensor is an intelligent one). You want to write a C program that will read that data and either buffer it, and retain only last (you did not say...) and at the same time will wait for requests from a Python script to give it back what it has received (and kept) from the sensor. That probably means a dual thread program with quite a bit of synchronization.
You will also need to specify the communication way between C and Python. You can certainly use the subprocess module, but do not forget to use unbuffered output in C. But you could also imagine an independant program that uses a FIFO or a named piped with a well defined protocol for external requests, in order to completely separate both problems.
So my opinion is that this is currently too broad for a single SO question...
Hey everyone I have a large scope type question that I'd really appriciate feedback/insight on.
I'm a newish programer and am Developing an 'Engine Development Enviorment' for fun at work. I have a program that makes alot of run files, and I have another program that manages batched/local multiprocessed simulations.
I want them to work seamlessly together, but I only want one instance of the 'BatchMaster' to run locally (from the taskbar). I also do alot of scripting type stuff for exploratory data analysis and would love the ability to launch simulations in a single line of code like the following.
import enginemodels
aetd = enginemodels.aetd(bleed='ON')
results = aetd.run(altitude=80000,mach=5,tempsls=60)
I'm would like to have my engine model run method send input to the 'BatchMaster' process.
My question is two parts:
1) How to do you find a multiprocessing instance in windows and send it information?
2) If there isn't an instance of that program, how do you launch it?
Thanks for any feedback or insight you can provide!
This will really help out alot of people at my workplace who aren't good at programming, and do most of their work making files via copy paste.
I would like to write a tiny calendar-like application for someone as a birthday present (to be run on Ubuntu). All it should do is display a separate picture each day, so whenever it's invoked it should check the date and select the appropriate picture from the collection I would provide, but also, in case it just keeps running, it should switch to the next picture when the next day begins.
The date-checking on invocation isn't the problem; my question pertains to the second case: how can I have the program notice the beginning of the next day? My clumsy approach would be to make it check the current date at regular intervals and let it change the displayed picture once there was a change in date, but that strikes me as very roundabout and not particularly elegant.
In case any of you have got some idea of how I could accomplish this, please don't hesitate to reply. I would aim to write the application in either Perl or Python, so suggestions concerning those two languages would be most welcome, but any other suggestions would be appreciated as well.
Thanks a lot for your time!
The answer to this could be very system dependant. Controlling the time at which your program is executed is likely to be system dependant. On all *nix type systems, I would use cron. Assuming for a moment that you are using a *nix system, the answer then depends on what the program actually does.
If it only needs to select an image, then I would suggest that it not be run continuously, but terminates itself after selecting it, and is then run again the next day (there are a lot of tutorials on how to setup cron).
If, however, it has some form of UI and it is likely (read possible) to keep running for several days, then you can follow two approaches:
Create your program as it is, to poll periodically for the current time, and do a date delta comparison. Python timedelta objects could help here. This is pretty much your inelegant approach.
The other solution would be to send it a signal from cron when you do wish it to update. This process would mean that you would have to make it signal aware, and respond to something like USR1. The Python docs talk to this, but you can find many tutorials on the web. This approach also works quite nicely for daemonised apps.
I'm sure there are many other approaches too, but those are the ones that come to mind for a quickish and nastyish app.
Did you think about scheduling the invoke of your script?
For me, the best approach is this:
1.Have two options to run the script:
run_script
run_script --update
2.Schedule the update run in some task scheduler (for example Cron) to be executed daily.
3.When you would want to check the image for current day, simply run the script without update option.
If you would like me to extend any part of these, simply ask about it.
Update : For anyone wondering what I went with at the end -
I divided the result-set into 4 and ran 4 instances of the same program with one argument each indicating what set to process. It did the trick for me. I also consider PP module. Though it worked, it prefer the same program. Please pitch in if this is a horrible implementation! Thanks..
Following is what my program does. Nothing memory intensive. It is serial processing and boring. Could you help me convert this to more efficient and exciting process? Say, I process 1000 records this way and with 4 threads, I can get it to run in 25% time!
I read articles on how python threading can be inefficient if done wrong. Even python creator says the same. So I am scared and while I am reading more about them, want to see if bright folks on here can steer me in the right direction. Muchos gracias!
def startProcessing(sernum, name):
'''
Bunch of statements depending on result,
will write to database (one update statement)
Try Catch blocks which upon failing,
will call this function until the request succeeds.
'''
for record in result:
startProc = startProcessing(str(record[0]), str(record[1]))
Python threads can't run at the same time due to the Global Interpreter Lock; you want new processes instead. Look at the multiprocessing module.
(I was instructed to post this as an answer =p.)