Detecting --help of a subcommand

[smurfix]

In my @group command(s) I do some basic processing (read config file for mandatory option et al). The problem is that I don't want to do any of that when a subcommand is invoked with --help; I want to show the subcommand help to the user, not the complaint about a missing config file.

Is there a way to do that, other than to dig through sys.argv?

[swilcox]

Short answer: there's no public flag on Context for "the subcommand is going to show --help". When your group callback runs, Click has already split off the subcommand name but hasn't parsed its options yet — so the --help token is still sitting in the not-yet-parsed tail, not on ctx. You have two clean options that don't touch sys.argv:

1. Don't do the work eagerly (the idiomatic fix)

Move config loading into ctx.obj as a loader, and let each subcommand pull it when it actually needs it:

class Config:
    def __init__(self):
        self._loaded = False
        self.data = None
    def load(self):
        if not self._loaded:
            self.data = read_config_file()  # may raise
            self._loaded = True

@click.group()
@click.pass_context
def cli(ctx):
    ctx.obj = Config()        # cheap; never fails

@cli.command()
@click.pass_obj
def run(config):
    config.load()             # only runs for real invocations, not --help

--help on any subcommand short-circuits before the subcommand body runs, so load() is never called. This also handles arbitrary nesting (mycli grp sub --help) for free.

2. Peek at the staged args via a Group subclass

If you really want the group callback itself to skip work, override Group.invoke and look at the args that have been staged for the subcommand. They live on the context as ctx._protected_args + ctx.args at that point:

class HelpAwareGroup(click.Group):
    def invoke(self, ctx):
        remaining = list(ctx._protected_args) + list(ctx.args)
        ctx.meta["help_requested"] = any(
            a in ctx.help_option_names for a in remaining[1:]
        )
        return super().invoke(ctx)

@click.group(cls=HelpAwareGroup)
@click.pass_context
def cli(ctx):
    if ctx.meta.get("help_requested"):
        return
    load_config(...)

This stays inside Click's own parsed data (so it honors a customized help_option_names) and doesn't reach into sys.argv. Caveat: _protected_args is underscored and the public protected_args property is deprecated for Click 9.0, so option (1) is the more durable recommendation.