Using argparse to parse arguments of form “arg= val”

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 ach

Answer 1

@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 2

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)

Answer 3

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 4

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.