Slides from my talk at the Stockholm Python User Group's meetup on Best Practices on October 31st, 2013: http://www.meetup.com/pysthlm/events/145658462/

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