Is there a way to implement **kwargs behavior when calling a Python script from the command line

Question

Say I have a function as follows:

def foo(**kwargs):
    print kwargs

And then call the function like this, I get this handy little dict of all kwargs.

>>> foo(a = 5, b = 7)
{'a': 5, 'b': 7}

I want to do this directly to scripts I call from command line. So entering this:

python script.py a = 5 b = 7

Would create a similar dict to the example above. Can this be done?

Here's what I have so far:

import sys

kwargs_raw = sys.argv[1:]
kwargs = {key:val for key, val in zip(kwargs_raw[::3], kwargs_raw[1::3])}
print kwargs

And here's what this produces:

Y:\...\Python>python test.py a = 5 b = 7
{'a': '5', 'b': '7'}

So you may be wondering why this isn't good enough

1. Its very structured, and thus, won't work if a or b are anything other that strings, ints, or floats.
2. I have no way of determining if the user intended to have 5 be an int, string, or float

I've seen ast.literal_eval() around here before, but I couldn't figure out how to get that to work. Both my attempts failed:

>>> ast.literal_eval("a = 5")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "Y:\admin\Anaconda\lib\ast.py", line 49, in literal_eval
    node_or_string = parse(node_or_string, mode='eval')
  File "Y:\admin\Anaconda\lib\ast.py", line 37, in parse
    return compile(source, filename, mode, PyCF_ONLY_AST)
  File "<unknown>", line 1
    a = 5

and

>>> ast.literal_eval("{a:5,b:7}")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "Y:\admin\Anaconda\lib\ast.py", line 80, in literal_eval
    return _convert(node_or_string)
  File "Y:\admin\Anaconda\lib\ast.py", line 63, in _convert
    in zip(node.keys, node.values))
  File "Y:\admin\Anaconda\lib\ast.py", line 62, in <genexpr>
    return dict((_convert(k), _convert(v)) for k, v
  File "Y:\admin\Anaconda\lib\ast.py", line 79, in _convert
    raise ValueError('malformed string')
ValueError: malformed string

If it matters, I'm using Python 2.7.6 32-bit on Windows 7 64-bit. Thanks in advance

Answer 1

It seems what you're really looking for is a way to parse command-line arguments. Take a look at the argparse module: http://docs.python.org/2/library/argparse.html#module-argparse

Alternately, if you really want to give your arguments in dictionary-ish form, just use the json module:

import json, sys

# Run your program as:
# python my_prog.py "{'foo': 1, 'bar': 2}"
# (the quotes are important)
data = json.loads(sys.argv[1])