Is it ‘allowed’ to get parameters like this

[Cecil Westerhof]

On Thursday 11 Aug 2016 16:29 CEST, Peter Otten wrote:

> Cecil Westerhof wrote:
>
>> It has been a while since I worked with Python. I wanted to get
>> some stats about the idle time of my computer, so that was a good
>> moment to pick up Python again. ;-)
>>
>>
>> As I understood it getopt is the way to get the parameters for your
>> script. But at the moment it looks a bit like overkill, my script
>> does not have much parameters as parameter_error shows: def
>> parameter_error(): print('Error: {0} [ --5 | --10 | --20 | --25 ]
>> --all | --this-month | --this-year | --today'
>> .format(basename(sys.argv[0]))) sys.exit(1)
>>
>> So at the moment this is my init function:
>> def init():
>> global conn
>> global cursor
>> global vmstat_params
>>
>> arg_length = len(sys.argv)
>> if   (arg_length == 1):
>> period       = '--today'
>> slice_length = 20
>> elif (arg_length == 2):
>> period       = sys.argv[1]
>> slice_length = 20
>> elif (arg_length == 3):
>> period = sys.argv[2]
>> if (sys.argv[1] in ['--5', '--10', '--20', '--25']):
>> slice_length = int(sys.argv[1][2:])
>> else:
>> parameter_error()
>> else:
>> parameter_error()
>
> <snip>
>
> Contrast that with the following cli based on argparse:
>
> $ cat demo.py
> #!/usr/bin/env python3
>
> def init():
> import argparse
>
> parser = argparse.ArgumentParser()
> parser.add_argument(
> "period", nargs="?",
> choices="today this-month this-year all".split(),
> default="today",
> help="Period covered")
> parser.add_argument(
> "slice_length", type=int, nargs="?",
> choices=[5, 10, 20, 25],
> default=20,
> help="Whatever...")
>
> print(parser.parse_args())
>
> init() $ ./demo.py -h usage: demo.py [-h]
> [{today,this-month,this-year,all}] [{5,10,20,25}]
>
> positional arguments:
> {today,this-month,this-year,all}
> Period covered
> {5,10,20,25}          Whatever...
>
> optional arguments: -h, --help show this help message and exit $
> ./demo.py all Namespace(period='all', slice_length=20) $ ./demo.py
> none usage: demo.py [-h] [{today,this-month,this-year,all}]
> [{5,10,20,25}] demo.py: error: argument period: invalid choice:
> 'none' (choose from 'today', 'this-month', 'this-year', 'all') $
> ./demo.py all 5 Namespace(period='all', slice_length=5) $ ./demo.py
> all 7 usage: demo.py [-h] [{today,this-month,this-year,all}]
> [{5,10,20,25}] demo.py: error: argument slice_length: invalid
> choice: 7 (choose from 5, 10, 20, 25)
>
> The interface is not exactly the same, but the code that defines it
> is declarative rather than trying to cover all possible combinations
> of input and should be easier to maintain in the long run.

That is very neat indeed. I am used of options starting with --, but I
am not married to that. I am going to look into this.


> Thus the answer to your question is no, the Python Police will have
> to arrest you if you stick with your original approach ;)

Luckily I am going to change the code. :-D

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof