startle 0.0.4

Instantly start a CLI from a function

startle

[!WARNING]
startle is alpha and should be considered unstable as its interface is fluid 😅, consider pinning to a version.

startle lets you transform a python function into a command line entry point, e.g:

wc.py:

from pathlib import Path
from typing import Literal

from startle import start


def word_count(
    fname: Path, /, kind: Literal["word", "char"] = "word", *, verbose: bool = False
) -> None:
    """
    Count the number of words or characters in a file.

    Args:
        fname: The file to count.
        kind: Whether to count words or characters.
        verbose: Whether to print additional info.
    """

    text = open(fname).read()
    count = len(text.split()) if kind == "word" else len(text)

    print(f"{count} {kind}s in {fname}" if verbose else count)


start(word_count)

❯ python wc.py --help:

When you invoke start, it will construct an argparser (based on type hints and docstring), parse the arguments, and invoke word_count.

❯ python wc.py wc.py -k char --verbose:

---

startle is inspired by Typer, and Fire, but some decisions are done differently:

• Use of positional-only or keyword-only argument separators (/, *, see PEP 570, 3102) are naturally translated into positional arguments or options.
• Like Typer and unlike Fire, type hints strictly determine how the individual arguments are parsed and typed.
• Short forms (e.g. -k, -v above) are automatically provided based on the initial of the argument.
• Variable length arguments are more intuitively handled. You can use --things a b c (in addition to --things=a --things=b --things=c).
• Like Typer and unlike Fire, help is simply printed and not displayed in pager mode by default, so you can keep referring to it as you type your command.
• Like Fire and unlike Typer, docstrings determine the description of each argument in the help text, instead of having to individually add extra type annotations. This allows for a very non-intrusive design, you can adopt (or un-adopt) startle with no changes to your function.
• *args but also **kwargs are supported, to parse unknown arguments as well as unknown options (--unk-key unk-val).