Using argparse to parse arguments of form “arg= va

Question

I want to use argparse to parse command lines of form "arg=val" For example, the usage would be:

script.py conf_dir=/tmp/good_conf

To achieve it, I am doing this:

desc   = "details"
parser = argparse.ArgumentParser(description=desc, add_help=False)
args = parser.add_argument("conf_dir")
args = parser.parse_args("conf_dir=FOO".split())
args = parser.parse_args()
print args.conf_dir

But, the problem is that, on invocation of the script with:

python script.py conf_dir=/tmp/good_conf

I get:

conf_dir=/tmp/good_conf

Where as I expect

/tmp/good_conf

So, the question is: Can I use argparse to parse cmd line, which contains name value pairs? Any hints?

Edit: The reason I want to do this and not some thing like --conf_dir=/tmp/good_dir is because there are other tools (written in other language), which uses conf_dir=/tmp/good_dir style of arguments. To maintain consistency, I was to parse args in this way.

Answer 1

The usual way to put name value pairs on the command line is with options. I.e. you would use

python script.py --confdir=/tmp/good_conf

argparse can certainly handle that case. See the docs at:

http://docs.python.org/library/argparse.html#option-value-syntax

Answer 2

@chepner This is great. I improved this to support multiple args as well and store the result as dict:

class StoreDict(argparse.Action):
    def __call__(self, parser, namespace, values, option_string=None):
        kv={}
        if not isinstance(values, (list,)):
            values=(values,)
        for value in values:
            n, v = value.split('=')
            kv[n]=v
        setattr(namespace, self.dest, kv)

Answer 3

As per the documentation, argparse doesn't natively let you have unprefixed options like that. If you omit the leading -, it assumes you are describing a positional argument and expects it to be provided as:

python script.py /tmp/good_conf

If you want it to be optional, it needs to be correctly marked as a flag by calling it --conf_dir, and invoking the script like:

python script.py --conf_dir=/tmp/good_conf

However, to accept name-value pairs, you can implement a custom action. In combination with nargs, such an action could accept an arbitrary number of name-value pairs and store them on the argument parsing result object.

Answer 4

You need a custom action

class StoreNameValuePair(argparse.Action):
    def __call__(self, parser, namespace, values, option_string=None):
        n, v = values.split('=')
        setattr(namespace, n, v)

args = parser.add_argument("conf_dir", action=StoreNameValuePair)