About

The python argparse module is powerful but eventually apps can easily accumulate a huge number of arguments that are a pain to specify every time. Thus, the simple answer to that is to add a configuration file. There are other python modules that try to merge argparse with configuration files, but none of them supports hierarchies well -- and if you're going to accept a configuration file, it should (IMHO) be well structured where modules can contain their own sections, etc. The ArgparseWithConfig class provides this interface.

It is intended as a drop-in replacement (a super class) of argparse, but I have no doubt there are missing features. Basic command options work, as do argument_groups. More is likely needed beyond that.

Important command line ordering philosophy

Arguments are processed in the following order, regardless of ordering on the command line:

1. defaults for the application
2. configuration file (--config) loaded overriding defaults (`--set-default``)
3. command line options are parsed, overriding both 1 and 2

Installation

pip install argparse-with-config

Usage

Basic drop in replacement with config dict

Just like standard argparse, but now there are some extra options:

    from argparse_with_config import ArgumentParserWithConfig
    parser = ArgumentParserWithConfig()

    parser.add_argument(
        "-d", "--dog", default="spike", help="bogus"
    )

    parser.add_argument(
        "-c", "--cat", default="mittens", help="cat name", config_path="kitty"
    )

    args = parser.parse_args(["-d", "spot"])

    print(args)
    # Namespace(config=None, set=None, dog='spot', cat='mittens')

    print(parser.config)
    # {'dog': 'spot', 'kitty': 'mittens'}

Note how the config tokens are mapped from the additional config_path flag.

Even more powerful: structured depths

What's better is that you can have (endless) sub-dicts with a better structure to isolate needed components together:

    from argparse_with_config import ArgumentParserWithConfig
    parser = ArgumentParserWithConfig()

    parser.add_argument(
        "-d", "--dog", default="spike", help="bogus", config_path="animals.dog"
    )

    parser.add_argument(
        "-c", "--cat", default="mittens", help="cat name", config_path="animals.kitty"
    )

    args = parser.parse_args(["-d", "spot"])

    print(args)
    # Namespace(config=None, set=None, dog='spot', cat='mittens')

    print(parser.config)
    # {'animals': {'dog': 'spot', 'kitty': 'mittens'}}

Note that the base Namespace is still the same, but the config now has a lot more structure to it.

Even more powerful: grouping to create depth

The above is basically also equivalent to:

from argparse_with_config import ArgumentParserWithConfig parser = ArgumentParserWithConfig()

    group = parser.add_argument_group("animals", config_path="animals")

    group.add_argument(
        "-d", "--dog", default="spike", help="bogus", config_path="dog"
    )

    group.add_argument(
        "-c", "--cat", default="mittens", help="cat name", config_path="kitty"
    )

    args = parser.parse_args(["-d", "spot"])

    print(args)
    # Namespace(config=None, set=None, dog='spot', cat='mittens')

    print(parser.config)
    # {'animals': {'dog': 'spot', 'kitty': 'mittens'}}

Use with configuration files

By default, two new arguments will be added to the command line:

• --config FILE...: loads configuration from a YAML configuration file
• --set name=val: Evaluates each expression for a left/right pair

Example configuration

Consider this yaml file:

---
bogus: 5000
animals:
    zebra: Marty
silent:
    ninja: deadly
something:
    wicked:
        thisway: comes

And this code base:

from argparse_with_config import ArgumentParserWithConfig
parser = ArgumentParserWithConfig()

group = parser.add_argument_group("animals", config_path="animals")

group.add_argument(
    "-d", "--dog", default="spike", help="bogus", config_path="dog"
)

group.add_argument(
    "-c", "--cat", default="mittens", help="cat name", config_path="kitty"
)

args = parser.parse_args(["-d", "goodboy", "--config", "test.yml"])

print(parser.config)
# {'animals': {'dog': 'goodboy', 'kitty': 'mittens'}}

Command line options override configuration files

Note that command line options always override configuration files, which are expected to be general defaults. Ordering does not matter. Thus, even though the --dog flag occurs before the --config flag, the --dog flag is given preference.

from argparse_with_config import ArgumentParserWithConfig
parser = ArgumentParserWithConfig()

group = parser.add_argument_group("animals", config_path="animals")

group.add_argument(
    "-d", "--dog", default="spike", help="bogus", config_path="dog"
)

group.add_argument(
    "-c", "--cat", default="mittens", help="cat name", config_path="kitty"
)

args = parser.parse_args(["--dog", "goodboy", "--config", "test.yml"])

print(parser.config)
# {'animals': {'dog': 'goodboy', 'kitty': 'mittens'}}

Using command line --set-default expressions

This also works with the --set-default flag:

from argparse_with_config import ArgumentParserWithConfig
parser = ArgumentParserWithConfig()

group = parser.add_argument_group("animals", config_path="animals")

group.add_argument(
    "-d", "--dog", default="spike", help="bogus", config_path="dog"
)

group.add_argument(
    "-c", "--cat", default="mittens", help="cat name", config_path="kitty"
)

args = parser.parse_args(["--set-default", "animals.cat=paws"])

print(parser.config)
# {'animals': {'kitty': 'paws', 'dog': 'spike'}}

TODO

There is a huge amount lef to do, but it is in a basic usable state today.

Left:

• more testing with other argparse features
• support many more argparse sub-classes where needed
• support reading multiple config types, including TOML and maybe json
• make parse_args return a super class of Namespace with a .config attribute?
• remove/fix some of the grosser hacks -- much is clean, but there are a couple of nasty hacks.

Related packages and information

• argparse_config
  • Uses a generic config structure -- I wanted something much more complex at times.
• A useful stack overflow and partial argument parsing
• (there was at least one more that I've lost track of)