pymcutil_execute.py

# (1) explicitly chained
commands.execute().chain(
    commands.execute.at(
        target=selectors.entities(type=entities.creeper))
).chain(
    commands.execute.unless_entity(
        target=selectors.entities(type=entities.ocelot, r=3))
).chain(
    commands.execute.if_block(
        position=(0, -1, 0), 
        block=blocks.grass)
).then(
    commands.summon(
        position=(0, 0, 0),
        entity=entities.ocelot))

# (2) up-front as a group
commands.execute(
    modifiers=(
        commands.execute.at(
            target=selectors.entities(type=entities.creeper)),
        commands.execute.unless_entity(
            target=selectors.entities(type=entities.ocelot, r=3)),
        commands.execute.if_block(
            position=(0, -1, 0), 
            block=blocks.grass)),
    command=commands.summon(
        position=(0, 0, 0),
        entity=entities.ocelot))

# (3) recursively, as subcommands of one another
commands.execute.at(
    target=selectors.entities(type=entities.creeper),
    subcommand=commands.execute.unless_entity(
        target=selectors.entities(type=entities.ocelot, r=3),
        subcommand=commands.execute.if_block(
            position=(0, -1, 0),
            block=blocks.grass,
            subcommand=commands.execute.then(
                command=commands.summon(
                    position=(0, 0, 0),
                    entity=entities.ocelot)))))