radicli 0.0.6

Radically lightweight command-line interfaces

radicli: Radically lightweight command-line interfaces

radicli is a small, zero-dependency Python package for creating command line interfaces, built on top of Python's argparse module. It introduces minimal overhead, preserves your original Python functions and uses type hints to parse values provided on the CLI. It supports all common types out-of-the-box, including complex ones like List[str], Literal and Enum, and allows registering custom types with custom converters.

Important note: This package aims to be a simple option based on the requirements of our libraries. If you're looking for a more full-featured CLI toolkit, check out typer, click or plac.

⏳ Installation

Note that radicli currently requires Python 3.8+.

pip install radicli

👩‍💻 Usage

The Radicli class sets up the CLI and provides decorators for commands and subcommands. The Arg dataclass can be used to describe how the arguments should be presented on the CLI. Types and defaults are read from the Python functions. You typically don't have to change anything about how you implement your Python functions to make them available as a CLI command.

# cli.py
from radicli import Radicli, Arg

cli = Radicli()

@cli.command(
    "hello",
    name=Arg(help="Your name"),
    age=Arg("--age", "-a", help="Your age"),
    greet=Arg("--greet", "-G", help="Whether to greet"),
)
def hello(name: str, age: int, greet: bool = False):
    """Description of the function for help text."""
    if greet:
        print(f"Hello {name} ({age})!")

if __name__ == "__main__":
    cli.run()

$ python cli.py hello Alex --age 35 --greet
Hello Alex (35)!

If a file only specifies a single command (with or without subcommands), you can optionally leave out the command name. So the above example script can also be called like this:

$ python cli.py Alex --age 35 --greet
Hello Alex (35)!

Subcommands

radicli supports one level of nested subcommands. The parent command may exist independently, but it doesn't have to.

@cli.subcommand("parent", "child1", name=Arg("--name", help="Your name"))
def parent_child1(name: str):
    ...

@cli.subcommand("parent", "child2", name=Arg("--age", help="Your age"))
def parent_child2(age: int):
    ...

$ python cli.py parent child1 --name Alex
$ python cli.py parent child2 --age 35

Working with types

For built-in callable types like str, int or float, the string value received from the CLI is passed to the callable, e.g. int(value). More complex, nested types are resolved recursively. The library also provides several built-in custom types for handling things like file paths.

⚠️ Note that there's a limit to what can reasonably be supported by a CLI interface so it's recommended to avoid overly complex types. For a Union type, the first type of the union is used. Optional types are expected to be left unset to default to None. If a value is provided, the type marked as optional is used, e.g. str for Optional[str].

Lists

By default, list types are implemented by allowing the CLI argument to occur more than once. The value of each element is parsed using the type defined for list members.

@cli.command("hello", fruits=Arg("--fruits", help="One or more fruits"))
def hello(fruits: List[str]):
    print(fruits)

$ python cli.py hello --fruits apple --fruits banana --fruits cherry
['apple', 'banana', 'cherry']

If you don't like this syntax, you can also add a converter to the Arg definition that handles the value differently, e.g. by splitting a comma-separated string. This would let the user write --fruits apple,banana,cherry, while still passing a list to the Python function.

Literals and Enums

Arguments that can only be one of a given set of values can be typed as a Literal. Any values not in the list will raise a CLI error.

@cli.command("hello", color=Arg("--color", help="Pick a color"))
def hello(color: Literal["red", "blue", "green"]):
    print(color)  # this will be a string

Enums are also supported and in this case, the enum key can be provided on the CLI and the function receives the selected enum member.

class ColorEnum(Enum):
    red = "the color red"
    blue = "the color blue"
    green = "the color green"

@cli.command("hello", color=Arg("--color", help="Pick a color"))
def hello(color: ColorEnum):
    print(color)  # this will be the enum, e.g. ColorEnum.red

Using custom types and converters

radicli supports defining custom converter functions to handle individual arguments, as well as all instances of a given type globally. Converters take the string value provided on the CLI and should return the value passed to the function, consistent with the type. They can also raise validation errors.

format_name = lambda value: value.upper()

@cli.command("hello", name=Arg("--name", converter=format_name))
def hello(name: str):
    print(f"Hello {name}"!)

$ python cli.py hello --name Alex
Hello ALEX!

Global converters for custom types

The converters argument lets you provide a dict of types mapped to converter functions when initializing Radicli. If an argument of that target type is encountered, the input string value is converted automatically. This ensures your Python functions remain composable and don't need additional logic only to satisfy the CLI usage.

The following example shows how to register a custom converter that loads a spaCy pipeline from a string name, while allowing the function itself to require the Language object itself:

import radicli
import spacy

def load_spacy_model(name: str) -> spacy.language.Language:
    return spacy.load(name)

converters = {spacy.language.Language: load_spacy_model}
cli = Radicli(converters=converters)

@cli.command(
    "process",
    nlp=Arg(help="The spaCy pipeline to use"),
    name=Arg("--text", help="The text to process")
)
def process_text(nlp: spacy.language.Language, text: str):
    doc = nlp(text)
    print(doc.text, [token.pos_ for token in doc])

$ python test.py process en_core_web_sm --text Hello world!
Hello world! ['INTJ', 'NOUN', 'PUNCT']

If you want to alias an existing type to add custom handling for it, you can create a NewType. This is also how the built-in Path converters are implemented. In help messages, the type it is based on will be displayed together with the custom name.

from typing import NewType
from pathlib import Path

ExistingPath = NewType("ExistingPath", Path)

def convert_existing_path(path_str: str) -> Path:
    path = Path(path_str)
    if not path.exists():
        raise ValueError(f"path does not exist: {path_str}")
    return path

converters = {ExistingPath: convert_existing_path}

Allowing extra arguments

If you want to capture and consume extra arguments not defined in the function and argument annotations, you can use the command_with_extra or subcommand_with_extra decorators. Extra arguments are passed to the function as a list of strings to an argument _extra (which you can change via the extra_key setting when initializing the CLI). spaCy uses this feature to pass settings to pip in its download command or to allow arbitrary configuration overrides during training.

@cli.command_with_extra("hello", name=Arg("--name", help="Your name"))
def hello(name: str, _extra: List[str] = []):
    print(f"Hello {name}!", _extra)

$ python cli.py hello --name Alex --age 35 --color blue
Hello Alex! ['--age', '35', '--color', 'blue']

Command aliases by stacking decorators

The command and subcommand decorators can be stacked to make the same function available via different command aliases. In this case, you just need to make sure that all decorators receive the same argument annotations, e.g. by moving them out to a variable.

args = dict(
    name=Arg(help="Your name"),
    age=Arg("--age", "-a", help="Your age")
)

@cli.command("hello", **args)
@cli.command("hey", **args)
@cli.subcommand("greet", "person", **args)
def hello(name: str, age: int):
    print(f"Hello {name} ({age})!")

$ python cli.py hello --name Alex --age 35
$ python cli.py hey --name Alex --age 35
$ python cli.py greet person --name Alex --age 35

🎛 API

dataclass Arg

Dataclass for describing argument meta information. This is typically used in the command decorators and only includes information for how the argument should be handled on the CLI. Argument types and defaults are read from the Python function.

Argument	Type	Description
option	Optional[str]	Option to use on the CLI, e.g. --arg. If unset, argument will be treated as positional.
short	Optional[str]	Shorthand for option, e.g. -A.
help	Optional[str]	Help text for argument, used for --help.
count	bool	Only count and return number of times an argument is used, e.g. --verbose or -vvv (for shorthand -v).
converter	Optional[Callable[[str], Any]]	Converter function that takes the string from the CLI value and returns a value passed to the function.

dataclass Command

Internal representation of a CLI command. Can be accessed via Radicli.commands and Radicli.subcommands.

Name	Type	Description
name	str	The name of the command.
func	Callable	The decorated command function.
args	List[ArgparseArg]	The internal representation of the argument annotations. Argparse.arg lets you access the original Arg.
description	Optional[str]	The command description, taken from the function docstring.
allow_extra	bool	Whether to allow extra arguments.
parent	Optional[str]	Name of the parent command if command is a subcommand.
display_name	str	The display name including the parent if available, e.g. parent child.

class Radicli

Attributes

Name	Type	Description
prog	Optional[str]	Program name displayed in --help prompt usage examples, e.g. "python -m spacy".
help	str	Help text for the CLI, displayed in top-level --help. Defaults to "".
version	Optional[str]	Version available via --version, if set.
converters	Dict[Type, Callable[[str], Any]]	Dict mapping types to global converter functions.
commands	Dict[str, Command]	The commands added to the CLI, keyed by name.
subcommands	Dict[str, Dict[str, Command]]	The subcommands added to the CLI, keyed by parent name, then keyed by subcommand name.

method Radicli.__init__

Initialize the CLI and create the registry.

from radicli import Radicli

cli = Radicli(prog="python -m spacy")

Argument	Type	Description
prog	Optional[str]	Program name displayed in --help prompt usage examples, e.g. "python -m spacy".
help	str	Help text for the CLI, displayed in top-level --help. Defaults to "".
version	Optional[str]	Version available via --version, if set.
converters	Dict[Type, Callable[[str], Any]]	Dict mapping types to converter functions. All arguments with these types will then be passed to the respective converter.
extra_key	str	Name of function argument that receives extra arguments if the command_with_extra or subcommand_with_extra decorator is used. Defaults to "_extra".

decorator Radicli.command, Radicli.command_with_extra

The decorator used to wrap top-level command functions.

@cli.command(
    "hello",
    name=Arg(help="Your name"),
    age=Arg("--age", "-a", help="Your age"),
    greet=Arg("--greet", "-G", help="Whether to greet"),
)
def hello(name: str, age: int, greet: bool = False) -> None:
    if greet:
        print(f"Hello {name} ({age})")

$ python cli.py hello Alex --age 35 --greet
Hello Alex (35)

@cli.command_with_extra(
    "hello",
    name=Arg(help="Your name"),
    age=Arg("--age", "-A", help="Your age"),
)
def hello(name: str, age: int, _extra: List[str]) -> None:
    print(f"Hello {name} ({age})", _extra)

$ python cli.py hello Alex --age 35 --color red
Hello Alex (35) ['--color', 'red']

Argument	Type	Description
name	str	Name of the command.
**args	Arg	Keyword arguments defining the argument information. Names need to match the function arguments. If no argument annotations are defined, all arguments are treated as positional.
RETURNS	Callable	The wrapped function.

decorator Radicli.subcommand, Radicli.subcommand_with_extra

The decorator used to wrap one level of subcommand functions.

@cli.subcommand("hello", "world", name=Arg(help="Your name"))
def hello_world(name: str) -> None:
    print(f"Hello world, {name}!")

$ python cli.py hello world Alex
Hello world, Alex!

@cli.subcommand_with_extra("hello", "world", name=Arg(help="Your name"))
def hello_world(name: str, _extra: List[str]) -> None:
    print(f"Hello world, {name}!", _extra])

$ python cli.py hello world Alex --color blue
Hello world, Alex! ['--color', 'blue']

Argument	Type	Description
parent	str	Name of the parent command (doesn't need to exist).
name	str	Name of the subcommand.
**args	Arg	Keyword arguments defining the argument information. Names need to match the function arguments.
RETURNS	Callable	The wrapped function.

method Radicli.placeholder

Add empty parent command with custom description text for subcommands without an executable parent.

cli.placeholder("parent", description="This is the top-level command description")

@cli.subcommand("parent", "child", name=Arg("--name", help="Your name"))
def child(name: str) -> None:
    print(f"Hello {name}!")

Argument	Type	Description
name	str	Name of the command.
description	Optional[str]	Command description for help texts.

method Radicli.run

Run the CLI. Typically called in a if __name__ == "__main__": block at the end of a file or in a package's __main__.py to allow executing the CLI via python -m [package].

if __name__ == "__main__":
    cli.run()

Argument	Type	Description
args	Optional[List[str]]	Optional command to pass in. Will be read from sys.argv if not set (standard use case).

Custom types and converters

The package includes several custom types implemented as TypeVars with pre-defined converter functions. If these custom types are used in the decorated function, the values received from the CLI will be converted and validated accordingly.

Name	Type	Description
ExistingPath	Path	Returns a path and checks that it exists.
ExistingFilePath	Path	Returns a path and checks that it exists and is a file.
ExistingDirPath	Path	Returns a path and checks that it exists and is a directory.
ExistingPathOrDash	Union[Path, Literal["-"]]	Returns an existing path but also accepts "-" (typically used to indicate that a function should read from standard input).
ExistingFilePathOrDash	Union[Path, Literal["-"]]	Returns an existing file path but also accepts "-" (typically used to indicate that a function should read from standard input).
ExistingDirPathOrDash	Union[Path, Literal["-"]]	Returns an existing directory path but also accepts "-" (typically used to indicate that a function should read from standard input).
PathOrDash	Union[Path, Literal["-"]]	Returns a path but also accepts "-" (typically used to indicate that a function should read from standard input).