Question or problem about Python programming:
I have written a Python script that checks a certain e-mail address and passes new e-mails to an external program. How can I get this script to execute 24/7, such as turning it into daemon or service in Linux. Would I also need a loop that never ends in the program, or can it be done by just having the code re executed multiple times?
How to solve the problem:
Solution 1:
You have two options here.
The python version 3.8 and the spyder3 IDE of python are used in this article to write the python script. You have to install spyder IDE in your system to use it. If you want to execute any script from the terminal, then run the ‘python’ or ‘python3’ command to open python in interaction mode. The following python script will print the text “Hello World” as output. Ability to download, install and set up Python packages from actions/python-versions that do not come preinstalled on runners. Allows for pinning to a specific patch version of Python without the worry of it ever being removed or changed. Automatic setup and download of Python packages if.
Make a proper cron job that calls your script. Cron is a common name for a GNU/Linux daemon that periodically launches scripts according to a schedule you set. You add your script into a crontab or place a symlink to it into a special directory and the daemon handles the job of launching it in the background. You can read more at Wikipedia. There is a variety of different cron daemons, but your GNU/Linux system should have it already installed.
Use some kind of python approach (a library, for example) for your script to be able to daemonize itself. Yes, it will require a simple event loop (where your events are timer triggering, possibly, provided by sleep function).
I wouldn’t recommend you to choose 2., because you would be, in fact, repeating cron functionality. The Linux system paradigm is to let multiple simple tools interact and solve your problems. Unless there are additional reasons why you should make a daemon (in addition to trigger periodically), choose the other approach.
Also, if you use daemonize with a loop and a crash happens, no one will check the mail after that (as pointed out by Ivan Nevostruev in comments to this answer). While if the script is added as a cron job, it will just trigger again.
Solution 2:
Here’s a nice class that is taken from here:
Solution 3:
- In addition to Kusalananda's answer, if you want the entire script to be run by python you can just change the first line to #!/usr/bin/env python3 and run it like any normal shell script. That way you don't have to remember what script you have to run with which interpreter.
- We would be using the below Python script to host it on the docker container. Lst = list lst = 'Python', 'Machine Learning', 'R Language', 'Bootstrap' for x in lst: print(x) In the above script, we have created a list and then iterated through a for loop to print the elements of the Python list.
You should use the python-daemon library, it takes care of everything.
From PyPI: Library to implement a well-behaved Unix daemon process.
Solution 4:
You can use fork() to detach your script from the tty and have it continue to run, like so:
Of course you also need to implement an endless loop, like
Hope this get’s you started.
Solution 5:
You can also make the python script run as a service using a shell script. First create a shell script to run the python script like this (scriptname arbitary name)
now make a file in /etc/init.d/scriptname
Now you can start and stop your python script using the command /etc/init.d/scriptname start or stop.
Hope this helps!
Execute Python scripts in the terminal or an IDE. Python files have the .py extension. Whenever you make a Python script, save it as name.py
A simple program (hello.py) is shown below. The first line indicates that we want to use the Python interpreter. The 3rd line outputs a line of text “hello wlrd” to the screen.
The text below can be copied into a text editor and save as hello.py. Python works with files that end in .py.
You can use any text editor to create a Python program. I recommend using a text editor that supports syntax highlighting (text colouring) and line numbers.
Related course:Complete Python Programming Course & Exercises
Run Python
Run from terminal
You can start a Python program with the terminal or command line. This works on all platforms (Mac OS, Windows, Linux).
To open a terminal on Windows: press the windows key + r key (run program), type cmd or command and press enter.
On Mac OS use finder to start a terminal. You can hit command+space and type terminal, then hit enter.
Start program
To start the program, we have to open the command line and type:
For this to work you need to be in the correct directory. That means, the directory where your python program is located.
On Mac OS and Linux you can see the current directory with the command pwd.
If you use Windows the directory is shown in the command line title bra.
To change directory use the command ‘cd’ like this ‘cd /home/user/pythonprojects’ or ‘cd C:Projects’.
Run from IDE
To run a Python script from an IDE, start a project first. Once the project is created add your .py files (or create them in the IDE) and press run.
In the PyCharm IDE:
- Start project
- Welcome screen opens, click Create New Project.
- On the main menu, choose File | New Project.
- Select Python interpreter
- Choose Python version from the list. Use 3.x
- Click create
- Add new Python file (File new) and add hello.py
- Click the green triangle to start the program. Another option is to click right mouse button on your Python file and selecting run.
Other IDEs have a similar process to run a Python program (start project, add file, run button).
Output
You should see a line of text showing “hello world”.
If you are a beginner, then I highly recommend this book.
Exercise
Python Script Runner Windows
Try the exercises below:
- Make a Python program that prints your name.
- Make a program that displays the lyrics of a song.
Python Script Runner Online
After completing these continue with the next exercise.