text: Title: Programmatically create tasks based on the product of the task executed in the previous pipeline step
  Body: I would like to understand how to programmatically create tasks based on the product of the task executed in the previous pipeline step. 
  
  For example, `get_data` creates csv-file and I want to create tasks for each row of csv: `process_row_1`, `process_row_2`, .... Accordingly, I have code using the python api that reads a csv-file -- how do I indicate that this csv-file is the product of another task? 
  So how do I use the upstream idiom (`upstream['get_data']`)?
  
  I formulate the question a brief, assuming that my case is quite typical. If this assumption of mine is incorrect, then I am ready to supplement the issue with code that more clearly illustrates my request.
  
  
  
  