Command line arguments that make you smile

Slides from my talk at the Stockholm Python User Group's meetup on best practices. Arguing that everyone should write more scripts, and when they do they should use the excellent docopt.

Transcript

1. Command line arguments that make you smile ! @martinmelin ! martin@tictail.com
2. Command line arguments that make you smile :-) ! @martinmelin ! martin@tictail.com
3. $ python --version Python 2.7.5
4. $ python --version Python 2.7.5
5. UI for your command-line program
6. Who still writes command-line programs?
7. Everyone should But we usually just call them scripts
8. Scripts are awesome Very few things are actually one-offs
9. One-off scripts spread knowledge Similar things can be solved by looking at old scripts
10. Scripts save you from yourself
11. $ one-off-script.py RuntimeError: Stupid mistake
12. Scripts are much better with arguments
13. $ one-off-script.py --dry-run RuntimeError: Stupid mistake
14. ... but adding arguments is painful, so we don’t
15. It doesn't have to be but first, the status quo:
16. argparse standard library recommendation
17. $ python prog.py -h usage: prog.py [-h] [--sum] N [N ...] ! Process some integers. ! positional arguments: N an integer for the accumulator ! optional arguments: -h, --help show this help message and exit --sum sum the integers (default: find the max)
18. Let’s parse!
19. import argparse ! parser = argparse.ArgumentParser( description='Process some integers.') !
20. import argparse ! parser = argparse.ArgumentParser( description='Process some integers.') ! parser.add_argument( 'integers', metavar='N', type=int, nargs='+', help='an integer for the accumulator') !
21. import argparse ! parser = argparse.ArgumentParser( description='Process some integers.') ! parser.add_argument( 'integers', metavar='N', type=int, nargs='+', help='an integer for the accumulator') ! parser.add_argument( '--sum', dest='accumulate', action='store_const', const=sum, default=max, help='sum the integers (default: find the max)') !
22. import argparse ! parser = argparse.ArgumentParser( description='Process some integers.') ! parser.add_argument( 'integers', metavar='N', type=int, nargs='+', help='an integer for the accumulator') ! parser.add_argument( '--sum', dest='accumulate', action='store_const', const=sum, default=max, help='sum the integers (default: find the max)') ! args = parser.parse_args()
23. import argparse ! parser = argparse.ArgumentParser( description='Process some integers.') ! parser.add_argument( 'integers', metavar='N', type=int, nargs='+', help='an integer for the accumulator') ! parser.add_argument( '--sum', dest='accumulate', action='store_const', const=sum, default=max, help='sum the integers (default: find the max)') ! args = parser.parse_args()
24. ... and we're done
25. Phew! ! All that ugly code for: prog.py [-h] [--sum] N [N ...]
26. There's a better way! Better practices™
27. docopt made by Vladimir Keleshev
28. $ python prog.py -h usage: prog.py [-h] [--sum] N [N ...] ! Process some integers. ! positional arguments: N an integer for the accumulator ! optional arguments: -h, --help show this help message and exit --sum sum the integers (default: find the max)
29. Let's parse!
30. """usage: prog.py [-h] [--sum] N [N ...] ! Process some integers. ! positional arguments: N an integer for the accumulator ! optional arguments: -h, --help show this help message and exit --sum sum the integers (default: find the max) """
31. """usage: prog.py [-h] [--sum] N [N ...] ! Process some integers. ! positional arguments: N an integer for the accumulator ! optional arguments: -h, --help show this help message and exit --sum sum the integers (default: find the max) """ import docopt
32. """usage: prog.py [-h] [--sum] N [N ...] ! Process some integers. ! positional arguments: N an integer for the accumulator ! optional arguments: -h, --help show this help message and exit --sum sum the integers (default: find the max) """ import docopt ! args = docopt.docopt(__doc__)
33. ... and we're done
34. $ python prog.py --sum 1 2 3 {'--help': False, '--sum': True, 'N': ['1', '2', '3']}
35. $ python prog.py --sum 1 2 3 {'--help': False, '--sum': True, 'N': ['1', '2', '3']} ! $ python prog.py --help usage: prog.py [-h] [--sum] N [N ...] ! Process some integers. ! positional arguments: N an integer for the accumulator ! optional arguments: -h, --help show this help message and exit --sum sum the integers (default: find the max)
36. Write for humans, let the computer figure it out
37. Write scripts !
38. Write scripts Use docopt
39. Write scripts Use docopt Smile :-)
40. Thanks! ! @martinmelin ! martin@tictail.com