When you are running python programs from the command line, you can pass various arguments to the program and your program can handle it.<\/p>\n\n\n\n
Here is a quick snippet of code that I will be explaining later:<\/p>\n\n\n\n
import sys\nif __name__ == \"__main__\":\n print(\"You passed: \", sys.argv)<\/code><\/pre>\n\n\n\nWhen you run this program from the command line, you will get this kind of results:<\/p>\n\n\n\n
$ python cmdargs.py\n You passed: ['cmdargs.py']<\/pre>\n\n\n\nNotice that the sys.argv<\/code> is an array of strings containing all arguments passed to the program. And the first value(at zeroth index) of this array is the name of the program itself. You can put all kinds of check on it.<\/p>\n\n\n\n\n\n\n\n$ python cmdargs.py 1 2 \"CloudxLab Inc\"\n You passed: ['cmdargs.py', '1', '2', 'CloudxLab Inc']<\/pre>\n\n\n\nWhy name check?<\/h2>\n\n\n\n
Please note that we are checking if the __name__<\/code> is equal to __main__<\/code> in order to avoid this code being executed when this file is included as a module.<\/p>\n\n\n\nThe following code also runs fine.<\/p>\n\n\n\n
import sys\nprint(\"You passed: \", sys.argv)<\/code><\/pre>\n\n\n\n$ python cmdargs.py\n You passed: ['cmdargs.py']<\/pre>\n\n\n\nIn python, you can include one python program in another program by using import. This is where the problem occurs.<\/p>\n\n\n\n
$ python\n Python 3.9.5 (default, May 4 2021, 03:36:27)\n [Clang 12.0.0 (clang-1200.0.32.29)] on darwin\n Type \"help\", \"copyright\", \"credits\" or \"license\" for more information.\nimport cmdargs<\/strong>\nYou passed: ['']<\/strong> <\/pre>\n\n\n\nNotice that the moment we imported cmdargs<\/code>, it ran our print statement. To avoid this code being executed during import, we put a check if the __name__<\/code> is equal to __main__<\/code>.<\/p>\n\n\n\nWhat about return value?<\/h2>\n\n\n\n
In Unix, every program returns a value to the operating system. In python, this is usually done by passing a signal in exit()<\/code> like this:<\/p>\n\n\n\nimport sys\nif __name__ == \"__main__\":\n print(\"You passed: \", sys.argv)\n exit(146)<\/code><\/pre>\n\n\n\nYou can check this by using `$?` special variable in shell.<\/p>\n\n\n\n
$ python cmdargs.py 1 2\n You passed: ['cmdargs.py', '1', '2']\n (venv) MacBook-Air:codefun sandeep$ echo $?\n 146<\/strong><\/pre>\n\n\n\nNotice that 146 being print by echo $?<\/code> As a matter of convention, in case of success, our program should return 0 and in case of failure, it should return a non-zero value.<\/p>\n\n\n\nParsing the command line<\/h2>\n\n\n\n
There is a very interesting module in Python which helps in parsing command line arguments called argparse<\/code><\/p>\n\n\n\nYou can utilize it to make your application handle really complex arguments. Here is a small snippet of code from a file create_screen_shots.py<\/code> where I used argparse<\/code> recently to do complex processing of arguments.<\/p>\n\n\n\nimport argparse\nif __name__ == \"__main__\":\n parser = argparse.ArgumentParser(description='Export notes from google slides. The files will be created per slide. The name will n.txt where n starts from 0.')\n parser.add_argument('slidesid', metavar='SlideId', type=str, help='The id of the Google Slide.')\n parser.add_argument('dir', metavar='Directory', type=str, help='The directory in which these screenshots will be saved.', nargs='?')\n parser.add_argument('total_slides', metavar='total_slides', type=int, help='Total Number of slides', nargs='?')\n \n args = parser.parse_args()\n # Do something with it\n print(args.slidesid, args.dir, args.total_slides )\n<\/code><\/pre>\n\n\n\nAs added bonus, it also provides a nice help manual to the user of my program.<\/p>\n\n\n\n
$ python create_screen_shots.py --help\n usage: create_screen_shots.py [-h] SlideId [Directory] [total_slides]\n Export notes from google slides. The files will be created per slide. The name will n.txt where n starts from 0.\n positional arguments:\n SlideId The id of the Google Slide.\n Directory The directory in which these screenshots will be saved.\n total_slides Total Number of slides\n optional arguments:\n -h, --help show this help message and exit<\/pre>\n\n\n\nYou can find out more about it in Python Doc of argparse.<\/a> <\/p>\n\n\n\nHappy Learning!<\/p>\n\n\n\n
You can experiment with and learn command-line arguments and various technologies using CloudxLab<\/a> without installing anything on your computer.<\/p>\n","protected":false},"excerpt":{"rendered":"