nested-argparse 💬 → 🅰.🅱.🆒

nested-argparse is a python module that non-invasively builds on top of the built-in argparse library to allow subparsers to parse into their own nested namespaces.

The library exposes a class NestedArgumentParser which allows arbitrary nesting without worry of namespace conflicts. This is achieved with the following principles of this library:

• Inversion of Control: A parser, when adding a subparser, is in control of what name to use for the sub-namespace which the subparser sends its parsed args to.
• Drop-In Replacement: The constructor for nested_argparse.NestedArgumentParser can be substituted in directly to where the constructor for argparse.ArgumentParser is being used. All subsequent method calls and subparser API calls should work without any additional code change!
• Customizeability: There are additional kwargs exposed to further customize the nesting options to your liking, if the defaults do not suit your scenario.

The main difference between this library and its built-in counterpart is the return value of the parse_args method. Instead of a flat namespace containing all parsed arguments across all subparsers, NestedArgumentParser will produce a namespace tree.

Simple Conceptual Example

Given the following parser:

Root Parser
 ├─ positional_1
 ├─ --optional_1
 ├─ --optional_2
 └─ sub parsers with dest='subcommand'
     ├─ Sub Parser 1 with name='sub1'
     │   ├─ --optional_1
     │   └─ --optional_2 with dest='optional2AltName'
     └─ Sub Parser 2 with name='sub2'
         ├─ --optional_1
         └─ --optional_2

And the following args to parse:

Alice --optional_1=Bob sub1 --optional_1=Carol --optional_2=David

The built-in ArgumentParser would not be able to handle the duplication in dests, but NestedArgumentParser will produce the following result when run through parse_args:

Namespace(
  subcommand='sub1',
  positional_1='Alice',
  optional_1='Bob',
  sub1=Namespace(
    optional_1='Carol',
    optional2AltName='David'
  )
)

API Documentation

The library exposes the following modules.

Module nested_argparse

The module exports the following classes.

Class NestedArgumentParser

• extends argparser.ArgumentParser
• for documentation for the superclass, see the official Python API reference docs for argparse.

Constructor

In addition to the parameters available to ArgumentParser constructor, the following parameters are also accepted:

• Param nest_dir, optional, type: Optional[str]

  • When a string is passed in, it is used as the attribute name in the parent namespace to which the nested namespace, where the parsed values will be stored, is assigned to.
  • When None is passed in, no nested namespace is created, and parsed values are directly assigned to the parent namespace. This is the behavior of the base ArgumentParser.
  • Default value: None.

• Param nest_separator, optional, type: str

  • It is used as the separator to delimit components in the nest path when representing the path as a string (for example, this is used to generate dests)
  • Default value: '__'.

• Param nest_path, optional, type: Optional[List[str]]

  • When a list of strings is passed in, it is used as a sequence of nested attribute names from the parent namespace which locates the nested namespace where the parsed values will be stored.
  • When None is passed in, no nested namespace is created, and parsed values are directly assigned to the parent namespace. This is the behavior of the base ArgumentParser.

Override NestedArgumentParser.add_argument

Instead of adding an argument definition which stores the parsed value to dest in the flat top-level namespace, the parsed value will be stored at attribute with the name given by dest in the namesapce at the nesting path associated with this parser.

Override NestedArgumentParser.add_subparsers

The return value of this method is an instance of internal subparser handler _NestedSubParsersAction, which exposes extra options for adding subparsers.

Override NestedArgumentParser.parse_args

The return value of this method is a namespace tree rather than a flat namespace. The tree is built according to the nesting paths associated with each of the parsed values.

Override NestedArgumentParser.parse_known_args

The return value of this method is a namespace tree rather than a flat namespace. The tree is built according to the nesting paths associated with each of the parsed values.

Class _NestedSubParsersAction

Override _NestedSubParsersAction.add_parser

• Param nest_dir, optional, type: Optional[str]
  • When a string is passed in, it is used as the attribute name in the parent namespace to which the subparser will store its parsed values to.
  • When None is passed in, the dest field is used as the nesting directory instead.
  • Default value: None.