Develop Reference

Python program should still run even when system sleeps [Uuntu]

I'd like to keep my Python program running, even when my computer is sleeping. The python program should not stop even when the system sleeps.
I am using a Ubuntu.
My file is only on my computer, not online.
Please help me out to achieve this.
If you need more information, please leave a comment!

Short Answer -
No! you can't.
Details -
Sleep Mode is a power-saving state that is similar to pausing a DVD movie, all applications on the computer are suspended and there is no setting to change this. If you set the machine to sleep, then all programs are suspended. Sleep mode and hibernation both simply save the state your desktop is in (what programs are open, what files are accessed) in a file that is saved in RAM or on the hard drive respectively. But the computer is then put into a low power state.

Python script stops running when screen turns off

I am trying to do a simple bot in Python, I have written the body and I wanted to try it on real data. So I ran it, it runs in an infinite loop and at the end of the loop it sleeps for 6 seconds because it gets data from server and needs to sleep so it does not get kicked from server. Anyway, by the time I sat in front of the PC and was doing my stuff the script was running (I am running it from Windows command prompt) but when I turned off the screen and came back, the script was not running anymore. I have tried this few times with different lengths of the runs of script and always it stopped after i turned off the screen.
How to keep python script running once the computer screen is turned off

Check "Power Options" in the Control panel.
You don't need to worry about the screen locking or turning off as these wont affect running processes in python. However, if your system is set to sleep after a set amount of time you may need to change this to Never. Keep in mind there are separate settings depending on whether or not the system is plugged in.

Change "Battery saver" mode to "Best Performance" mode.
This worked for me, in continue running the scripts when screen turned off

Methods to schedule a task prior to runtime

What are the best methods to set a .py file to run at one specific time in the future? Ideally, its like to do everything within a single script.
Details: I often travel for business so I built a program to automatically check me in to my flights 24 hours prior to takeoff so I can board earlier. I currently am editing my script to input my confirmation number and then setting up cron jobs to run said script at the specified time. Is there a better way to do this?
Options I know of:
• current method
• put code in the script to delay until x time. Run the script immediately after booking the flight and it would stay open until the specified time, then check me in and close. This would prevent me from shutting down my computer, though, and my machine is prone to overheating.
Ideal method: input my confirmation number & flight date, run the script, have it set up whatever cron automatically, be done with it. I want to make sure whatever method I use doesn't include keeping a script open and running in the background.

cron is best for jobs that you want to repeat periodically. For one-time jobs, use at or batch.

Uploading code to server and run automatically

I'm fairly competent with Python but I've never 'uploaded code' to a server before and have it run automatically.
I'm working on a project that would require some code to be running 24/7. At certain points of the day, if a criteria is met, a process is started. For example: a database may contain records of what time each user wants to receive a daily newsletter (for some subjective reason) - the code would at the right time of day send the newsletter to the correct person. But of course, all of this is running out on a Cloud server.
Any help would be appreciated - even correcting my entire formulation of the problem! If you know how to do this in any other language - please reply with your solutions!
Thanks!

Here are two approaches to this problem, both of which require shell access to the cloud server.
Write the program to handle the scheduling itself. For example, sleep and wake up every few miliseconds to perform the necessary checks. You would then transfer this file to the server using a tool like scp, login, and start it in the background using something like python myscript.py &.
Write the program to do a single run only, and use the scheduling tool cron to start it up every minute of the day.

Took a few days but I finally got a way to work this out. The most practical way to get this working is to use a VPS that runs the script. The confusing part of my code was that each user would activate the script at a different time for themselves. To do this, say at midnight, the VPS runs the python script (using scheduled tasking or something similar) and runs the script. the script would then pull times from a database and process the code at those times outlined.
Thanks for your time anyways!

How to pause a python script running in terminal

I have a web crawling python script running in terminal for several hours, which is continuously populating my database. It has several nested for loops. For some reasons I need to restart my computer and continue my script from exactly the place where I left. Is it possible to preserve the pointer state and resume the previously running script in terminal?
I am looking for a solution which will work without altering the python script. Modifying the code is a lower priority as that would mean to relaunch the program and reinvest time.
Update:
Thanks for the VM suggestion. I'll take that. For the sake of completion, what generic modifications should be made to script to make it pause and resumable?
Update2:
Porting on VM works fine. I have also modified script to make it failsafe against network failures. Code written below.

You might try suspending your computer or running in a virtual machine which you can subsequently suspend. But as your script is working with network connections chances are your script won't work from the point you left once you bring up the system. Suspending a computer and restoring it or saving a Virtual M/C and restoring it would mean you need to restablish the network connection. This is true for any elements which are external to your system and network is one of them. And there are high chances that if you are using a dynamic network, the next time you boot chances are you would get a new IP and the network state that you were working previously would be void.
If you are planning to modify the script, few things you need to keep it mind.
Add serializing and Deserializing capabilities. Python has the pickle and the faster cPickle method to do it.
Add Restart points. The best way to do this is to save the state at regular interval and when restarting your script, restart from last saved state after establishing all the transients elements like network.
This would not be an easy task so consider investing a considrable amount of time :-)
Note***
On a second thought. There is one alternative from changing your script. You can try using cloud Virtualization Solutions like Amazon EC2.

I ported my script to VM and launched it from there. However there were network connection glitches after resuming from hibernation. Here's how I solved it by tweaking python script:
import logging
import socket
import time
socket.setdefaulttimeout(30) #set timeout in secs
maxretry = 10 #set max retries
sleeptime_between_retry = 1 #waiting time between retries
erroroccured = 0
while True:
try:
domroot = parse(urllib2.urlopen(myurl)).getroot()
except Exception as e:
erroroccured += 1
if erroroccured>maxretry:
logger.info("Maximum retries reached. Quitting this leg.")
break
time.sleep(sleeptime_between_retry)
logging.info("Network error occurred. Retrying %d time..."%(erroroccured))
continue
finally:
#common code to execute after try or except block, if any
pass
break
This modification made my script temper proof to network failures.

As others have commented, unless you are running your script in a virtual machine that can be suspended, you would need to modify your script to track its state.

Since you're populating a database with your data, I suggest to use it as a way to track the progress of the script (get the latest URL parsed, have a list of pending URLs, etc.).
If the script is terminated abruptly, you don't have to worry about saving its state because the database transactions will come to the rescue and only the data that you've committed will be saved.
When the script is retarted, only the data for the URLs that you completely processed will be stored and you it can resume just picking up the next URL according to the database.

If this problem is important enough to warrant this kind of financial investment, you could run the script on a virtual machine. When you need to shut down, suspend the virtual machine, and then shut down the computer. When you want to start again, start the computer, and then wake up your virtual machine.

WinPDB is a python debugger that supports remote debugging. I never used it, and don't know if remote debugging a running process requires a modification to the script (which is very likely, otherwise it'd be a security issue); but if remote debugging without modifying the script is possible then you may be able to dump the current state of the script to a file and figure out later how to load it. I don't think it would work though.