# Design notes

## Why doesn’t OCRmyPDF use PyTesseract?

PyTesseract is a Python wrapper around the Tesseract OCR engine. When OCRmyPDF was first written, PyTesseract used ABI bindings to call the Tesseract library. This was not a good fit for OCRmyPDF because ABI bindings can be fragile.

PyTesseract has since evolved calling the Tesseract executable, abandoning the ABI approach and using the CLI instead, just like OCRmyPDF does. If it were written from scratch today, OCRmyPDF might use PyTesseract.

PyTesseract has more features don’t particularly need PDF output, but less features than OCRmyPDF’s API for creating PDFs.

## What is `executor()`?

OCRmyPDF uses a custom concurrent executor which can support either threads or processes with the same interface. This is useful because OCRmyPDF can use either threads or processes to parallelize work, whichever is more appropriate for the task at hand.

The interface is currently private and subject to change. In particular, if experiments with asyncio and anyio are successful, the interface will change.