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CLI Patterns

Advanced patterns and techniques for building CLIs with params-proto.

Grouped Options with Prefixes

Use @proto.prefix to organize related parameters into logical groups:

python
@proto.prefix
class Model:
  """Model architecture."""
  name: str = "resnet50"
  hidden_size: int = 256

@proto.prefix
class Training:
  """Training hyperparameters."""
  lr: float = 0.001
  batch_size: int = 32

@proto.cli
def main(seed: int = 42):
  """Train model."""
  pass

Generated help:

usage: main.py [-h] [--seed INT] [OPTIONS]

Train model.

options:
  -h, --help              show this help message and exit
  --seed INT              Random seed (default: 42)

Model options:
  Model architecture.

  --Model.name STR        Model name (default: resnet50)
  --Model.hidden-size INT Hidden size (default: 256)

Training options:
  Training hyperparameters.

  --Training.lr FLOAT        Learning rate (default: 0.001)
  --Training.batch-size INT  Batch size (default: 32)

This groups options visually and makes help text more readable for complex CLIs with many parameters.

Benefits

  • Organization - Related parameters grouped together
  • Readability - Help text clearly shows which parameters belong together
  • Discoverability - Users can find related options easily
  • Scalability - Works well with many parameters

See Advanced Patterns for more on prefixes and singleton behavior.

Custom Program Name

Override the program name displayed in help text:

python
@proto.cli(prog="train_model")
def train(lr: float = 0.001):
  """Train a model."""
  pass

Generated help:

usage: train_model [-h] [--lr FLOAT]

Without prog, uses the script filename from sys.argv[0].

Use Cases

  • Wrapped scripts - When your script is called via a wrapper or alias
  • Clarity - Set a clearer name than the actual filename
  • Documentation - Use a name that matches your documentation

Testing Help Generation

Access generated help text programmatically for testing and documentation:

python
@proto.cli
def train(lr: float = 0.001):
  """Train a model."""
  pass

# Plain text (for testing, logs, pipes)
print(train.__help_str__)

# Colorized (for terminal display)
print(train.__ansi_str__)

Use Cases

  • Unit tests - Verify help text is generated correctly
  • Documentation generation - Extract help text for docs
  • Debugging - Inspect what users will see
  • CI/CD - Validate help output in pipelines

Example Test

python
def test_help_text():
  @proto.cli
  def train(lr: float = 0.001):
    """Train a model."""
    pass

  help_text = train.__help_str__
  assert "--lr" in help_text
  assert "FLOAT" in help_text
  assert "default: 0.001" in help_text

Edge Cases

Long Parameter Names

Long parameter names are automatically wrapped in help text:

python
@proto.cli
def train(
  this_is_a_very_long_parameter_name: int = 1000,
):
  """Train with long names."""
  pass

Generated help (wraps nicely):

--this-is-a-very-long-parameter-name INT
                     This is a very long parameter name (default: 1000)

Numbers in Names

Numbers are preserved in parameter names and converted properly:

python
@proto.cli
def train(
  model_2d: bool = False,      # → --model-2d
  resnet50_pretrained: bool = True,  # → --resnet50-pretrained
):
  pass

Numbers remain in both the parameter name and the CLI argument, making it easy to reference models by version or variant.

Nested Dataclass Configuration

Override fields in nested dataclasses using dot notation:

python
from dataclasses import dataclass, field

@dataclass
class ModelConfig:
  hidden_size: int = 256
  num_layers: int = 4

@dataclass
class TrainConfig:
  epochs: int = 100
  model: ModelConfig = field(default_factory=ModelConfig)

@proto.cli
def main(config: TrainConfig):
  """Train with nested config."""
  print(f"epochs={config.epochs}")
  print(f"model.hidden_size={config.model.hidden_size}")

CLI usage:

bash
# Override top-level and nested fields
python train.py train-config --epochs 200 --model.hidden-size 512 --model.num-layers 8

Output:

epochs=200
model.hidden_size=512
model.num_layers=8

Benefits

  • Deep nesting - Works with arbitrary nesting depth (--model.encoder.layers)
  • Type conversion - Nested fields are converted to their annotated types
  • Kebab-case - Use --model.hidden-size (kebab) for hidden_size (snake)

Quick Pattern Reference

PatternWhen to UseExample
Basic CLISimple scripts with few parameters@proto.cli def train(lr: float = 0.001)
Grouped OptionsMany related parametersUse @proto.prefix classes for organization
Nested ConfigsHierarchical configurationUse nested dataclasses with dot notation
Custom Program NameWrapped scripts or clarity@proto.cli(prog="my-tool")
TestingVerify help outputAccess __help_str__ attribute

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