AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Resources:
  Bucket:
    Type: AWS::S3::Bucket     
  Function:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: s3://bucketname/object.zip # Add in an S3 URI where you have code Lambda Code
      Runtime: python3.7
      Handler: index.handler
      Policies:
        - Version: 2012-10-17
          Statement: 
            - Effect: Allow
              Action: s3:GetObject*
              Resource: !Sub "arn:aws:s3:::${Bucket}*"
      Events:
        Upload:
          Properties:
            Bucket:
              Ref: Bucket
            Events: s3:ObjectCreated:*
          Type: S3