Different value of `inject` in ansible lookup plugins. In the first case, `inject` is a dictionary with host/group/fact data, in the second case, its a function.

mytest.py

# Place in lookup_plugins/foo/mytest.py

from ansible import utils

class LookupModule(object):

    def __init__(self, basedir=None, **kwargs):
        self.basedir = basedir

    def run(self, terms, inject=None, **kwargs):
        terms = utils.listify_lookup_plugin_terms(terms, self.basedir, inject)
        ret = []

        if not isinstance(terms, list):
            terms = [ terms ]

        for term in terms:
            ret.append(repr(inject)) # This is what we're interested in

        return ret

output

$ ansible-playbook -c local -i localhost, test.yml

PLAY [all] ********************************************************************

GATHERING FACTS ***************************************************************
ok: [localhost]

TASK: [debug msg={{item}}] ****************************************************
ok: [localhost] => (item={'delegate_to': None, u'ansible_en1': ....<snipped, there is a bunch of fact/host/group data here>'})

TASK: [debug msg=<built-in function vars>] ************************************
ok: [localhost]

PLAY RECAP ********************************************************************
localhost                  : ok=3    changed=0    unreachable=0    failed=0

test.yml

---
  - hosts: all

    tasks:
    - debug: msg={{ item }}
      with_mytest: foo

    - debug: msg={{ lookup('mytest','foo') }}