Ansible Dynamic Inventory - generate inventory with ip addresses under specific tag with underscore instead of dot

[Berlin]

I am new to Ansible. When I am using `ec2.py` dynamic inventory to generate inventory, after the playbook is finished to run, the results are shown as list of IP addresses under specific tag with underscore instead of dot. 

For example I want to run a playbook on instances with specific tag, I wonder how other people work with IP addresses? 

    ---

    - hosts: tag_test_staging

      sudo: true

      tasks:

      - name: Make sure that we can connect to the machine

        ping:

    

    PLAY RECAP *********************************************************************

    10_80_20_47                : ok=0    changed=0    unreachable=1    failed=0 

For private address, ec2.ini:

    hostname_variable = private_ip_address

    destination_variable = private_ip_address

    vpc_destination_variable = private_ip_address

The results from ec2.py:

     "tag_test_staging": [

        "10_80_20_47"

      ],

For Public Address, ec2.ini:

    hostname_variable = ip_address

    destination_variable = public_dns_name

    vpc_destination_variable = ip_address

The results from ec2.py:

     "tag_test_staging": [

        "52_28_11_11"

      ],

[Berlin]

It works if I comment out the hostname_variable, because it allow to override the inventory_name with an ec2 variable, instead of using the destination_variable

    #hostname_variable = private_ip_address
    #hostname_variable = ip_address
    destination_variable = public_dns_name
    vpc_destination_variable = private_ip_address

For Private IPs:

    destination_variable = private_ip_address