[Tutor] command line list arguments

[Garry Willgoose]

I want to input a python list as a command line argument as for example

python weathering-sens.py -daughter ['p0-50-50','p0-0-0-100’]

but what I get from sys.argv is [p0-50-50,p0-0-0-100] without the string delimiters on the list elements. I’m probably missing something really simple because sys.argv returns strings and probably strips the string delimiters in that conversion … but is there any way that I can keep the string delimiters so that inside the code I can just go (if arg is ['p0-50-50','p0-0-0-100’])

a=eval(arg)

or is there no alternative to doing this

python weathering-sens.py -daughter 'p0-50-50’ 'p0-0-0-100’

and doing the legwork of interpreting all the arguments individually (I’ve seen an example of this on the web).





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[Chris Warrick]

On 7 November 2015 at 02:56, Garry Willgoose

Post by Garry Willgoose
I want to input a python list as a command line argument as for example
python weathering-sens.py -daughter ['p0-50-50','p0-0-0-100’]
but what I get from sys.argv is [p0-50-50,p0-0-0-100] without the string delimiters on the list elements. I’m probably missing something really simple because sys.argv returns strings and probably strips the string delimiters in that conversion … but is there any way that I can keep the string delimiters so that inside the code I can just go (if arg is ['p0-50-50','p0-0-0-100’])
a=eval(arg)
or is there no alternative to doing this
python weathering-sens.py -daughter 'p0-50-50’ 'p0-0-0-100’
and doing the legwork of interpreting all the arguments individually (I’ve seen an example of this on the web).

1. NEVER use eval().
2. Trying to pass Python code as arguments looks bad. Don’t do that.
3. Your issues with '' are caused by your shell. You would need to
wrap your entire thing in quotes first, or use escaping. But instead,
4. Use argparse or another argument parsing solution, and implement it
with two arguments.

[Peter Otten]

Post by Garry Willgoose
I want to input a python list as a command line argument as for example
python weathering-sens.py -daughter ['p0-50-50','p0-0-0-100’]
but what I get from sys.argv is [p0-50-50,p0-0-0-100] without the string
delimiters on the list elements. I’m probably missing something really
simple because sys.argv returns strings and probably strips the string
delimiters in that conversion … but is there any way that I can keep the
string delimiters so that inside the code I can just go (if arg is
['p0-50-50','p0-0-0-100’])
a=eval(arg)
or is there no alternative to doing this
python weathering-sens.py -daughter 'p0-50-50’ 'p0-0-0-100’
and doing the legwork of interpreting all the arguments individually (I’ve
seen an example of this on the web).

With argparse it's really not that much legwork:

$ cat weathering-sens.py
import argparse
parser = argparse.ArgumentParser()
parser.add_argument("-d", "--daughter", nargs="+")
args = parser.parse_args()
print(args.daughter)

$ python weathering-sens.py -d foo bar
['foo', 'bar']

$ python weathering-sens.py --daughter p0-50-50 p0-0-0-100
['p0-50-50', 'p0-0-0-100']

Note that args.daughter is a list of strings -- no need for eval().

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