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

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"
  ],

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

StackExchange DevOps Q#313, answer score: 5