up vote 1 down vote favorite

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?

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  • python-docopt is a command line argument parsing module. check it out! github.com/docopt/docopt – scarecrow Jun 13 '13 at 12:07
  • @anandaseelan -- Then all of the commandline arguments need to be known up-front ... – mgilson Jun 13 '13 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 Jun 13 '13 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 Jun 13 '13 at 13:06
  • @mgilson I expect to have well defined syntax, like --foo=23. – tamasgal Jun 13 '13 at 13:48
up vote 2 down vote accepted

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.

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  • globals().update(d) is the type of thing that got php into lots of bother – John La Rooy Jun 13 '13 at 13:07
  • @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. – mgilson Jun 13 '13 at 13:11
  • I'd be more concerned about the possibility of shadowing the builtins. – John La Rooy Jun 13 '13 at 13:14
  • @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. – mgilson Jun 13 '13 at 13:15
up vote 3 down vote

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)
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