Not able ping instances using dynamic inventory

I have downloaded ec2.py and ec2.ini files and placed them under

/etc/ansible/inventory

and i have changed the ansible.cfg to

inventory      = /etc/ansible/inventory/ec2.py

i have environment variables set up as

export AWS_ACCESS_KEY_ID="XXXXXXXXXXXXXXX"
export AWS_SECRET_ACCESS_KEY="XXXXXXXXXXXXXXXXXXXXX"
export AWS_DEFAULT_REGION="us-east-1"
export EC2_INI_PATH="/etc/ansible/inventory/ec2.ini"

now when i run ansible -m ping all i am getting

[WARNING]: provided hosts list is empty, only localhost is available

instead of pinging all instances in my account

What do you see when start ec2.py just as python application?
If you see your instances, may be you need to use:

inventory = /etc/ansible/inventory/

Thanks you so much for your help the issue has been resolved.

run the script /etc/ansible/inventory/ec2.py directly and see what output you get.