$ python setup.py build
$ python setup.py install

$ vim get_users
#!/usr/bin/python

import pwd
import cfengine3

if __name__ == '__main__':

    cf3 = cfengine3.protocol()
    users = [ user[0] for user in  pwd.getpwall() ]
    cf3.classes('system_users','define')
    cf3.scalar('count', '%s' % len(users))
    cf3.list('users', users)

$ vim example-module.cf
body common control {
    bundlesequence  => { "load", "run" };
}

bundle agent load {
    commands:
        "$(sys.workdir)/modules/get_users" module => "true";

    reports:
        system_users::
            "This machine has $(get_users.count) users in /etc/passwd";
}

bundle agent run {
    vars:
        "users" slist => { @(get_users.users) };

    reports:
        system_users::
          "user: $(users)";
}

$ cp examples/get_users /var/cfengine/modules/
$ cf-agent -KI -f $PWD/example-module.cf 
 -> Executing '/var/cfengine/modules/get_users' ...(timeout=-678,owner=-1,group=-1)
M "/var/cfengine/modules/get_users":
 -> Completed execution of /var/cfengine/modules/get_users
R: This machine has 36 users in /etc/passwd
R: user: root
R: user: daemon
R: user: bin
R: user: sys
....