# argparse_subcommand
Library to extend Python argparse stdlib with easy handling of subcommands
Extends `argparse.ArgumentParser` with a facility for configuring subcommands by convention.
Each subcommand lives in its separate Python module.
The name of the subcommand is the module name (without superpackage names)
with underscore replaced by dash.
To be a subcommand module, a module must have
```
import argparse_subcommand as ap_sub
meaning = "some help text for the subcommand"
def add_arguments(parser: ap_sub.ArgumentParser): ... # configure the subcommand's sub-argparser
def execute(args: ap_sub.Namespace): ... # run the subcommand
```
The module can also _optionally_ have:
```
aliases = ["subcmd-alias1", "subcmd-alias2"] # optional.
```
for making available the same subcommand under one or more
alternative names (e.g. an abbreviation).
For use, create the parser as usual and then call the submodule scanner:
```
def main(argv: list[str]):
parser = ap_sub.ArgumentParser(epilog=explanation)
parser.scan("mysubcmds.subcmd1", "mysubcmds.subcmd2") # or provide module object instead of str
args = parser.parse_args(argv[1:])
parser.execute_subcommand(args) # or supply nothing, then parse_args() will be called internally
if __name__ == '__main__':
main(sys.argv)
```
By convention, the subcommand modules (and only they) all go into a common package.
If you do that, you can scan them all at once:
```
parser.scan("mysubcmds.*", strict=True)
```
`argparse_subcommand` uses only one sub-parser group, so that
subcommands cannot be nested, there is only one level of subcommands.
It will execute `importlib.import_module()` on all modules mentioned in a `scan()` call as strings.
Multiple calls to `scan()` are allowed, each can have one or more arguments.
`scan(..., strict=False)` (the default) will ignore non-subcommand modules.
`scan(..., trace=True)` produces output helpful for debugging your subcommands setup.
That's all.
## Version history
- 1.0, 2023-05:
First release
- 1.1, 2024-01:
Error messages and trace messages go to stderr, not stdout.
More informative messages when scanned modules are non-subcommand modules.
Small improvements to documentation.
Added version history.
- 1.2, 2024-03:
Better and clearer pattern for the main routine in the documentation.
- ...
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