If you want to create a brand new serverless python 3 service you type...
$ serverless create --template aws-python3 --name myproject --path myproject
Docker is needed for the plugin serverless-python-requirements.
$ sls plugin install -n serverless-python-requirements
$ npm install --save serverless-dynamodb-local
$ sls dynamodb install
$ npm install serverless-offline-python --save-dev
export AWS_SDK_LOAD_CONFIG=1
sls deploy --aws-profile [aws profile]
$ sls offline start
Then you can access DynamoDB web shell at http://localhost:8000/shell/
At the time of this writing 08-20-2018 there's an issue with the serverless-dynamodb-local plugin with version 0.2.31, seems like downgrading to 0.2.30 fixes the issue, refer to this issue to see how to fix it.