Ctypes and Threads
Check out this ctypes technique to escape the GIL.
Fast Hand Detection
HAAR wavelets are by far the most popular way of detecting hands or other features, the problem is speed, the Haar cascade can easily take a single core to 100% usage, and this is not suitable if we plan to run this hand detector within another program like Blender or RealXtend and maintain good performance.
Another method that is faster is to check for convexity defects of contours, this blog by Andol has a good overview of the techniques. Using the heuristic 4 or more defects is hand, and simply checking for defects among the many contour passes will yield false-positives from noise. The first trick is to filter out this noise on the contour with extreme polygon reduction, using the function cv.ApproxPoly with a factor of 20-30.0 or more. This reduces the head to a few triangles, while keeping the star-shape of the hand.