Ansible callback plugin to print the number of remaining hosts in a task

output.txt

changed: [localhost3]
4 hosts remaining: localhost0, localhost1, localhost2, localhost4
changed: [localhost2]
3 hosts remaining: localhost0, localhost1, localhost4
changed: [localhost1]
2 hosts remaining: localhost0, localhost4
changed: [localhost0]
1 hosts remaining: localhost4
changed: [localhost4]
All hosts complete

remaining_hosts.py

from __future__ import (absolute_import, division, print_function)
__metaclass__ = type

from ansible import constants as C
from ansible.plugins.callback import CallbackBase

try:
    from __main__ import cli
except ImportError:
    cli = None


class CallbackModule(CallbackBase):
    CALLBACK_VERSION = 2.0
    CALLBACK_TYPE = 'aggregate'
    CALLBACK_NAME = 'remaining_hosts'

    def __init__(self, display=None):

        self.disabled = False

        if cli:
            self._options = cli.options
        else:
            self._options = None

        try:
            self.forks = self._options.forks
        except:
            self.forks = C.DEFAULT_FORKS

        self.play_hosts = []
        self.remaining = []

        super(CallbackModule, self).__init__(display=display)

    def v2_playbook_on_play_start(self, play):
        self.play = play
        play_vars = play._variable_manager.get_vars(play._loader,
                                                    play=self.play)
        self.play_hosts = play_vars['ansible_play_hosts']
        self.remaining = self.play_hosts[:]

    def v2_runner_on_ok(self, result, **kwargs):
        host = result._host.name
        self.remaining.remove(host)
        if self.remaining:
            self._display.display(
                '%d hosts remaining: %s' % (len(self.remaining),
                                           ', '.join(self.remaining))
            )
        else:
            self._display.display('All hosts complete')

    v2_runner_on_failed = v2_runner_on_ok
    v2_runner_on_unreachable = v2_runner_on_ok
    v2_runner_on_skipped = v2_runner_on_ok