pyclig

A Python Click wrapper with Command Line Interface Guidelines (CLIG) paradigms.

click owns parsing, help, shell completion & the test runner. pyclig adds the conventions on top: STDOUT for output & STDERR for messages, exit codes, error rendering, logging, output primitives & standard flags. Options, arguments & types are plain click.

Usage

import click
import pyclig

from dkais import exceptions


@pyclig.group(
    "dkais",
    short_help="DMA AIS data manager",
    examples=["dkais list --start 2026-10"],
    errors=(exceptions.Error,),
    epilog="For more information see https://github.com/andyrids/dkais.",
)
def cli() -> None:
    """Download DMA AIS archives and convert them to Parquet."""


@cli.command("list")
@pyclig.options.json_output()
@click.option("--start", metavar="DATE")
@pyclig.pass_context
def list_(ctx: pyclig.Context, start: str | None, json_output: bool) -> int:
    """List bucket archives & local state."""
    ctx.out.print(f"from {start}")
    return pyclig.ExitCode.OK


if __name__ == "__main__":
    cli()

Point the entry point at the group: [project.scripts] dkais = "dkais.__main__:cli". Always name the group - the name is the program name, also under python -m, and sets the shell completion variable (_DKAIS_COMPLETE).

What every group gets

ctx.obj is left to the application.

Errors & exit codes

Commands return an exit code (or None for 0). Anything else is mapped by the runner, with messages on STDERR:

pyclig.ExitCode names the codes: OK, FAILURE, USAGE, INTERNAL & INTERRUPT. The bug report hint names the distribution's Issues project URL. Messages are never parsed as Rich markup: user input such as [/b] or :warning: prints as typed.

A command may catch Ctrl-C or its own errors to print a tailored message first - a returned code passes through untouched. Wrap third-party failures (e.g. network errors) in an errors= type, so users see a message instead of a crash.

Output

ctx.out (STDOUT) & ctx.err (STDERR) are Rich consoles created for each run, with markup, emoji codes & highlighting off. Pass ctx.err to any Progress or Status. Each console follows its own stream: FORCE_COLOR, TTY_COMPATIBLE & NO_COLOR are honoured, and piped output on Windows keeps its colour when forced.

Arguments after the console are keyword-only. Control characters, including terminal escapes, are dropped from messages. Print machine-readable output - JSON, tab-separated rows - with click.echo, which neither wraps nor expands tabs. Use rich.text.Text with a style for styled output, and TextColumn(markup=False) in a Rich Progress.

Standard flags

pyclig.options holds the flags with standard names, each taking a help= override:

Logging

Log through the package logger - logging.getLogger(__name__) in any module of the package that defines the group. Libraries add only a NullHandler, in the package __init__.py:

logging.getLogger(__name__).addHandler(logging.NullHandler())

During a run, warnings & errors print as warning: / error: notices on ctx.err. With -d, a RichHandler adds DEBUG records, times ([2026-10-31T18:44:45+0000]) & call sites. The logger's handlers, level & propagation are restored when the run ends.

Testing

from pyclig.testing import invoke


def test_list_rows_when_piped() -> None:
    """Assert `list` prints tab-separated rows when STDOUT is a pipe."""
    result = invoke(cli, ["list"], out_tty=False, err_tty=True)
    assert result.exit_code == 0
    assert "\t" in result.stdout

invoke returns click's Result, with stdout & stderr apart. out_tty, err_tty, color & width set up each console; env sets (or, with None, unsets) variables. Colour & terminal variables from the developer's shell are cleared. Never patch Rich private attributes.

Parser-less entry points

pyclig.run() gives a pre-commit hook shim, which leaves sys.argv to the tool it wraps, the same exit codes, error rendering & logging:

def ruff_format() -> NoReturn:
    pyclig.run(
        lambda: core_ruff_format(sys.argv[1:]),
        errors=(exceptions.Error,),
    )

Migrating from argparse

• Each subcommand becomes a @cli.command(); shared options become one decorator stacking click.options. Commands are listed in the order they are added.
• click shows a command's docstring as its help: put \f after the help paragraph, so the Args: & Returns: sections stay out of --help. Pass help= for a description that is not an imperative docstring line.
• Custom argument types become click.ParamType[T] subclasses calling self.fail().
• parser.error() becomes raise click.UsageError(...) (or ctx.fail()).
• A type= function checking a minimum becomes click.IntRange(min=1).
• An environment variable default becomes envvar=, with show_envvar=True so a missing value names it.
• Module-level consoles become ctx.out / ctx.err, passed to helpers as arguments.
• argparse accepted unambiguous option prefixes (--st for --start); click does not.