How can I get a list of hosts from an Ansible inventory file?

Do the same trick from before, but instead of all, pass the group name you want to list:

ansible (group name here) -i (inventory file here) --list-hosts

I was struggling with this as well for awhile, but found a solution through trial & error.

One of the key advantages to the API is that you can pull variables and metadata, not just hostnames.

Starting from Python API - Ansible Documentation:

#!/usr/bin/env python
#  Ansible: initialize needed objects
variable_manager = VariableManager()
loader = DataLoader()

#  Ansible: Load inventory
inventory = Inventory(
    loader = loader,
    variable_manager = variable_manager,
    host_list = 'hosts', # Substitute your filename here
)

This gives you an Inventory instance, which has methods and properties to provide groups and hosts.

To expand further (and provide examples of Group and Host classes), here's a snippet I wrote which serializes the inventory as a list of groups, with each group having a 'hosts' attribute that is a list of each host's attributes.

#/usr/bin/env python
def serialize(inventory):
    if not isinstance(inventory, Inventory):
        return dict()

    data = list()
    for group in inventory.get_groups():
        if group != 'all':
            group_data = inventory.get_group(group).serialize()

            #  Seed host data for group
            host_data = list()
            for host in inventory.get_group(group).hosts:
                host_data.append(host.serialize())

            group_data['hosts'] = host_data
            data.append(group_data)

    return data

#  Continuing from above
serialized_inventory = serialize(inventory)

I ran this against my lab of four F5 BIG-IP's, and this is the result (trimmed):

<!-- language: lang-json -->
[{'depth': 1,
  'hosts': [{'address': u'bigip-ve-03',
             'name': u'bigip-ve-03',
             'uuid': UUID('b5e2180b-964f-41d9-9f5a-08a0d7dd133c'),
             'vars': {u'hostname': u'bigip-ve-03.local',
                      u'ip': u'10.128.1.130'}}],
  'name': 'ungrouped',
  'vars': {}},
 {'depth': 1,
  'hosts': [{'address': u'bigip-ve-01',
             'name': u'bigip-ve-01',
             'uuid': UUID('3d7daa57-9d98-4fa6-afe1-5f1e03db4107'),
             'vars': {u'hostname': u'bigip-ve-01.local',
                      u'ip': u'10.128.1.128'}},
            {'address': u'bigip-ve-02',
             'name': u'bigip-ve-02',
             'uuid': UUID('72f35cd8-6f9b-4c11-b4e0-5dc5ece30007'),
             'vars': {u'hostname': u'bigip-ve-02.local',
                      u'ip': u'10.128.1.129'}},
            {'address': u'bigip-ve-04',
             'name': u'bigip-ve-04',
             'uuid': UUID('255526d0-087e-44ae-85b1-4ce9192e03c1'),
             'vars': {}}],
  'name': u'bigip',
  'vars': {u'password': u'admin', u'username': u'admin'}}]