Here’s some blog posts I have written:
DataBlocks API: https://medium.com/@amaarora/fastai-v2-datablocks-api-code-overview-a-gentle-introduction-60338a6c9aa
DataSource: https://medium.com/@amaarora/data-source-datasource-true-76423298af2e
TfmdList: https://medium.com/@amaarora/fastai-tfmdlists-5feae9e8f42d
PipeLines: https://medium.com/@amaarora/fastai-pipelines-2d737df3da49