Command line arguments as variable definition in Python

Question

I'm trying to construct a (kind of template/wrapper) script, which is called with some undefined options

> the_script.py --foo=23 --bar=42 --narf=fjoord

which then creates a variable called foo=23, bar=42, narf='fjoord' inside it.

What's the way to do it? I tried with getopt, but it needs a second parameter, so I have to define which options to get and of course, I want to be able to define my variable names via command line. I tried OptionParser too, not sure how to deal with undefined options though.

So is the way manually parsing the sys.argv, or is there maybe a module out there, which does exactly the same thing?

python-docopt is a command line argument parsing module. check it out! github.com/docopt/docopt — scarecrow
– scarecrow, Commented Jun 13, 2013 at 12:07
@anandaseelan -- Then all of the commandline arguments need to be known up-front ... — mgilson
– mgilson, Commented Jun 13, 2013 at 12:34
Just curious -- What do you expect to do with the commandline options once you have them? Is the syntax always --foo=23, or could it be --foo 23? — mgilson
– mgilson, Commented Jun 13, 2013 at 12:35
It seems like a bad idea to have your script depend on its invocation to create variable names that it will reference. — chepner
– chepner, Commented Jun 13, 2013 at 13:06
@mgilson I expect to have well defined syntax, like --foo=23. — tamasgal
– tamasgal, Commented Jun 13, 2013 at 13:48

gspoosi · Accepted Answer · 2013-06-13 13:02:00Z

3

Use this. Maybe you need some string '' brackets some where...

>>python yourfunc.py foo=4 abc=5

import sys 
list=sys.argv[1:]
for i in list:
   exec(i)

edited Jun 13, 2013 at 13:02

answered Jun 13, 2013 at 12:53

gspoosi

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mgilson · Accepted Answer · 2013-06-13 13:28:54Z

2

This is a relatively simple task with ast.literal_eval and string splitting -- But only if you have a really well defined syntax. (e.g. only 1 of --foo=bar or --foo bar is allowed).

import argparse
import ast

parser = argparse.ArgumentParser() #allow the creation of known arguments ...

namespace,unparsed = parser.parse_known_args()

def parse_arg(arg):
    k,v = arg.split('=',1)
    try:
        v = ast.literal_eval(v) #evaluate the string as if it was a python literal
    except ValueError:          #if we fail, then we keep it as a string
        pass

    return k.lstrip('-'),v

d = dict(parse_arg(arg) for arg in unparsed)
print(d)

I've put the key-value pairs in a dictionary. If you really want them as global variables, you could do globals().update(d) -- But I would seriously advise against that.

edited Jun 13, 2013 at 13:28

answered Jun 13, 2013 at 12:39

mgilson

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4 Comments

John La Rooy Over a year ago

globals().update(d) is the type of thing that got php into lots of bother

mgilson Over a year ago

@gnibbler -- Like I said, I seriously advise against that. The only way to figure out what variables you have defined in that case is to inspect the globals() dictionary anyway ... Might as well just keep a separate dict around and use it.

John La Rooy Over a year ago

I'd be more concerned about the possibility of shadowing the builtins.

mgilson Over a year ago

@gnibbler -- Yeah, I suppose that's fair. Although you should find out pretty quickly with a "sum is not callable" type of error for most things.

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