Better help message with optional dataclasses #368

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1. mauvilsa commented on Sep 4, 2023

   

   mauvilsa

   on Sep 4, 2023

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   @bilelomrani1 thanks for pointing this out. Certainly there should be a way to get the details of the dataclass. This should be similar to how it is being done for subclasses. Though there are two cases to handle:

   • Optional dataclasses, e.g. Optional[DataClass]
   • Mixture of classes, e.g. Union[int, DataClass1, DataClass2, BaseForSubclasses1]

   In the first case it could be an argument --*.help that does not expect any value and would print the details for the dataclass. This means that for the example above, people would need to call the CLI as python main.py --config.help. Would be nicer if it were shown in the normal help, though this might be overly complicated to implement, since the parser wouldn't really have these arguments.

   For the second case, for certain it would be a --*.help that expects a class name or class import path. So the behavior would be just like it is now for subclasses.
2. bilelomrani1 commented on Sep 4, 2023

   

   bilelomrani1

   on Sep 4, 2023

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   Thank you @mauvilsa, great idea, adding an argument seems very reasonable to me indeed.
3. mauvilsa

   added

   enhancementNew feature or requestNew feature or request

   on Sep 6, 2023
4. jerrymatjila commented on Nov 17, 2023

   

   jerrymatjila

   on Nov 17, 2023

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   Here is the solution

   from dataclasses import dataclass
   from jsonargparse import ArgumentParser
   
   
   @dataclass
   class Config:
       a: int
       b: float = 2.0
   
   
   if __name__ == "__main__":
       parser = ArgumentParser()
       parser.add_argument("--config", type=Config)
       print(parser.parse_args())

   $ python example.py  -h
   usage: example.py [-h] [--config CONFIG] --config.a A [--config.b B]
   
   options:
     -h, --help       Show this help message and exit.
   
   Config(a: int, b: float = 2.0):
     --config CONFIG  Path to a configuration file.
     --config.a A     (required, type: int)
     --config.b B     (type: float, default: 2.0)

   To make meaningful help messages use docstrings as shown below

   from dataclasses import dataclass
   from jsonargparse import ArgumentParser
   from jsonargparse import set_docstring_parse_options
   set_docstring_parse_options(attribute_docstrings=True)
   
   @dataclass
   class Config:
       a: int
       """Number of integers."""
   
       b: float = 2.0
       """Number of floats."""
   
   
   if __name__ == "__main__":
       parser = ArgumentParser()
       parser.add_argument("--config", type=Config)
       print(parser.parse_args())

   $ python example.py  -h
   usage: example.py [-h] [--config CONFIG] --config.a A [--config.b B]
   
   options:
     -h, --help       Show this help message and exit.
   
   Config(a: int, b: float = 2.0):
     --config CONFIG  Path to a configuration file.
     --config.a A     Number of integers. (required, type: int)
     --config.b B     Number of floats. (type: float, default: 2.0)

   👎React with 👎1Reacted by Gabriel Belouze
5. mauvilsa

   added a commit that references this issue on Oct 9, 2025

   Argument to print help for dataclasses nested in types (#368).

   3403afb
6. mauvilsa

   closed this as completedin #783on Oct 9, 2025
7. mauvilsa commented on Oct 9, 2025

   

   mauvilsa

   on Oct 9, 2025

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   With pull request #783 just merged, the behavior is as proposed in #368 (comment). If there is a single nested dataclass, then there will be a --*.help option that doesn't expect any value. For multiple nested dataclasses, the --*.help option expects a class name or class path.