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 had a similar problem and I think nitzmahone’s approach of not using unsupported calls to the Python API. Here’s a working solution, relying on the nicely JSON-formatted output of ansible-inventory CLI:

pip install ansible==2.4.0.0 sh==1.12.14

An example inventory file, inventory/qa.ini:

[lxlviewer-server]
id-qa.kb.se

[xl_auth-server]
login.libris.kb.se

[export-server]
export-qa.libris.kb.se

[import-server]
import-vcopy-qa.libris.kb.se

[rest-api-server]
api-qa.libris.kb.se

[postgres-server]
pgsql01-qa.libris.kb.se

[elasticsearch-servers]
es01-qa.libris.kb.se
es02-qa.libris.kb.se
es03-qa.libris.kb.se

[tomcat-servers:children]
export-server
import-server
rest-api-server

[flask-servers:children]
lxlviewer-server
xl_auth-server

[apache-servers:children]
lxlviewer-server

[nginx-servers:children]
xl_auth-server

A Python 2.7 function to extract info (easily extendable to hostvars et cetera):

import json
from sh import Command

def _get_hosts_from(inventory_path, group_name):
    """Return list of hosts from `group_name` in Ansible `inventory_path`."""
    ansible_inventory = Command('ansible-inventory')
    json_inventory = json.loads(
        ansible_inventory('-i', inventory_path, '--list').stdout)

    if group_name not in json_inventory:
        raise AssertionError('Group %r not found.' % group_name)

    hosts = []
    if 'hosts' in json_inventory[group_name]:
        return json_inventory[group_name]['hosts']
    else:
        children = json_inventory[group_name]['children']
        for child in children:
            if 'hosts' in json_inventory[child]:
                for host in json_inventory[child]['hosts']:
                    if host not in hosts:
                        hosts.append(host)
            else:
                grandchildren = json_inventory[child]['children']
                for grandchild in grandchildren:
                    if 'hosts' not in json_inventory[grandchild]:
                        raise AssertionError('Group nesting cap exceeded.')
                    for host in json_inventory[grandchild]['hosts']:
                        if host not in hosts:
                            hosts.append(host)
        return hosts

Proof that it works (also with child and grandchild groups):

In [1]: from fabfile.conf import _get_hosts_from

In [2]: _get_hosts_from('inventory/qa.ini', 'elasticsearch-servers')
Out[2]: [u'es01-qa.libris.kb.se', u'es02-qa.libris.kb.se', u'es03-qa.libris.kb.se']

In [3]: _get_hosts_from('inventory/qa.ini', 'flask-servers')
Out[3]: [u'id-qa.kb.se', u'login.libris.kb.se']

In [4]:

For me following worked

from ansible.parsing.dataloader import DataLoader
from ansible.inventory.manager import InventoryManager

if __name__ == '__main__':
    inventory_file_name = 'my.inventory'
    data_loader = DataLoader()
    inventory = InventoryManager(loader = data_loader,
                             sources=[inventory_file_name])

    print(inventory.get_groups_dict()['spark-workers'])

inventory.get_groups_dict() returns a dictionary that you can use to get hosts by using the group_name as key as shown in the code.
You will have to install ansible package you can do by pip as follows

pip install ansible

There has been changes to Ansible API since the approved answer:

This works for Ansible 2.8 (and maybe more)

Here’s the way I was able to access most of the data:

from ansible.parsing.dataloader import DataLoader
from ansible.inventory.manager import InventoryManager


loader = DataLoader()
# Sources can be a single path or comma separated paths
inventory = InventoryManager(loader=loader, sources='path/to/file')

# My use case was to have all:vars as the 1st level keys, and have groups as key: list pairs.
# I also don't have anything ungrouped, so there might be a slightly better solution to this.
# Your use case may be different, so you can customize this to how you need it.
x = {}
ignore = ('all', 'ungrouped')
x.update(inventory.groups['all'].serialize()['vars'])
group_dict = inventory.get_groups_dict()

for group in inventory.groups:
    if group in ignore:
        continue
    x.update({
        group: group_dict[group]
    })

Example:

Input:

[all:vars]
x=hello
y=world

[group_1]
youtube
google

[group_2]
stack
overflow

Output:

{"x":"hello","y":"world","group_1":["youtube","google"],"group_2":["stack","overflow"]}

Again, your use case might be different than mine, so you’ll have to slightly change the code to how you want it to be.

With ansible 2.4 and more, use ansible-inventory executable.

With ansible 2.3 or less, use the following solution instead.

#! /usr/bin/python
# vi ansible-inventory
# Ansible 2.3- / Python 2.7 - use build-in Ansible Inventory 
import argparse
parser=argparse.ArgumentParser(description='List hosts in inventory as seen by Ansible.')
parser.add_argument('-i', dest='inventory_file', default=''
                   , help='Inventory filename', required=True)
args=parser.parse_args() ;
 
# For ansible 2.4, use this instead.
#from ansible.inventory.manager import Inventory
from ansible.parsing.dataloader import DataLoader
from ansible.inventory import Inventory
from ansible.vars import VariableManager

variable_manager=VariableManager()
data_loader=DataLoader()
inventory=Inventory(loader = data_loader 
                   , variable_manager=variable_manager
                   , host_list=args.inventory_file)
import json
print json.dumps(inventory.get_group_dict(), indent=4)

With this file in the path here above in $PATH as ansible-inventory, assuming inventory directory is production,

# ansible-inventory -i production