Conditional Parser

A flexible extension to Python’s ArgumentParser that enables dynamic, conditional command-line arguments - arguments that only appear based on the values of other arguments.

The argparse module is fantastic, but it lacks the ability to flexibly create conditional arguments. While the native ArgumentParser supports the ability to make a single subcommand, it does not have the ability to make multiple conditional arguments in parallel, in hierarchical structures, or with complex conditional logic. The ConditionalArgumentParser extends the native ArgumentParser to support these features while maintaining the familiar interface.

Contents:

• Installation
• Quick Start Guide
• Examples
• API Reference

Key Features

• Seamless extension of Python’s ArgumentParser

• Support for conditional arguments based on other argument values

• Hierarchical conditional dependencies

• Compatible with existing ArgumentParser usage

• Comprehensive help messages showing all possible arguments

• Clear documentation of when conditional arguments become available

Quick Example

Suppose your parser includes a --use-regularization flag for training a machine learning model. When this flag is used, you’d probably want to include another argument --regularizer-lambda to control the regularization strength - but this parameter is only relevant when regularization is enabled. With ConditionalArgumentParser, you can easily add this conditional argument.

from conditional_parser import ConditionalArgumentParser

parser = ConditionalArgumentParser()
parser.add_argument("--use-regularization", action="store_true")

# Will only add if --use-regularization is used
# E.g. if args.use_regularization == True
parser.add_conditional(
    "use_regularization", True, # parent / condition
    "--regularizer-lambda", # conditional argument
    # parameters for the conditional argument - these are totally normal!
    type=float,
    default=0.01
)

Design Note

This package does not work with subparsers. If you include a subparser, any conditional arguments will be ignored. I’m working on a solution for this, but it’s not yet implemented. Just note that if you need to use a subparser-like system, you can actually completely replace subparsers with conditional arguments, the API just looks a bit different. Here’s an example:

parser = ArgumentParser()
parser.add_argument("--no-subparsers-format", choices=["json", "csv"])
subparsers = parser.add_subparsers()

sub1 = subparsers.add_parser("command1")
sub1.add_argument("--format", choices=["json", "csv"])

# The above is (almost) equivalent to:
parser = ConditionalArgumentParser()
parser.add_argument("--no-subparsers-format", choices=["json", "csv"])
parser.add_argument("--subparser", type=str, choices=["command1"], required=False)
parser.add_conditional(
    "subparser",
    "command1",
    "--format",
    choices=["json", "csv"]
)