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Fix RichProgressBar loading when using LightningCLI #21340

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Fix RichProgressBar loading when using LightningCLI #21340

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Fix `RichProgressBar` loading when using `LightningCLI`
huangyxi Nov 6, 2025
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[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Nov 6, 2025
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3 changes: 3 additions & 0 deletions src/lightning/pytorch/callbacks/progress/rich_progress.py
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Original file line number Diff line number Diff line change
Expand Up @@ -221,6 +221,9 @@ class RichProgressBarTheme:
metrics_text_delimiter: str = " "
metrics_format: str = ".3f"

def __init__(self) -> None:
pass
Comment on lines +224 to +225
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@justusschock justusschock Nov 19, 2025

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it is unclear to me why this change is required. Data-classes generally don't require an init function

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@huangyxi huangyxi Nov 19, 2025

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The redundant __init__() here is just a workaround to ensure that jsonargparse or typeshed_client can correctly parse RichProgressBarTheme when it is used as the default argument to RichProgressBar in the CLI, as shown in the script above.

Without this workaround, the script throws a key-validation error:

$ python3 demo.py fit
usage: test.py [-h] [-c CONFIG] [--print_config[=flags]] {fit,validate,test,predict} ...
error: Validation failed: Parser key "rich_progress_bar.theme.progress_bar":
  Does not validate against any of the Union subtypes
  Subtypes: [<class 'str'>, <class 'rich.style.Style'>]
  Errors:
    - Expected a <class 'str'>. Got value: Not a valid subclass of Style. Got value: None
      Subclass types expect one of:
      - a class path (str)
      - a dict with class_path entry
      - a dict without class_path but with init_args entry (class path given previously)
    - Not a valid subclass of Style. Got value: Not a valid subclass of Style. Got value: None
      Subclass types expect one of:
      - a class path (str)
      - a dict with class_path entry
      - a dict without class_path but with init_args entry (class path given previously)
      Subclass types expect one of:
      - a class path (str)
      - a dict with class_path entry
      - a dict without class_path but with init_args entry (class path given previously)
  Given value type: <class 'ValueError'>
  Given value: Not a valid subclass of Style. Got value: None
  Subclass types expect one of:
  - a class path (str)
  - a dict with class_path entry
  - a dict without class_path but with init_args entry (class path given previously)

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@justusschock justusschock Nov 19, 2025

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yeah but then it should be a subclass of rich.style.Style actually and not a dataclass anymore

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@huangyxi huangyxi Nov 19, 2025

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I'm not familiar with the internal parsing mechanism, but as far as I know, either adding the redundant __init__() to this dataclass, or replacing all default values of arguments of RichProgressBarTheme typed Union[str, "Style"] with "" can solve this problem, where the latter one is clearly not ideal.

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@huangyxi huangyxi Nov 19, 2025

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The following fix correctly applies the options to the progress bar theme, but it still triggers a JsonargparseWarning (although it is no longer an error):

@dataclass
class RichProgressBarTheme:
    description: Union[str, "Style"] = ""
    progress_bar: Union[str, "Style"] = Style(color="#6206E0")
    progress_bar_finished: Union[str, "Style"] = Style(color="#6206E0")
    progress_bar_pulse: Union[str, "Style"] = Style(color="#6206E0")
    batch_progress: Union[str, "Style"] = ""
    time: Union[str, "Style"] = Style(dim=True)
    processing_speed: Union[str, "Style"] = Style(dim=True, underline=True)
    metrics: Union[str, "Style"] = Style(italic=True)
    metrics_text_delimiter: str = " "
    metrics_format: str = ".3f"

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@justusschock justusschock Nov 19, 2025

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@mauvilsa could you maybe advise what's the best way to go here? Adding an init function to a data-class seems not very pythonic to me.



class RichProgressBar(ProgressBar):
"""Create a progress bar with `rich text formatting <https://github.com/Textualize/rich>`_.
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