Python

I recently investigated our analysis code for the source of unwanted randomness. The culprit turned out to be the set-datatype in Python. For example, running following code produces varying order of the items between different runs:

idList = [ "ID" + str(i) for i in range(10) ]
idSet = set(idList)
print(idSet)

I asked the question in StackOverflow and in a few minutes jonrsharpe kindly pointed out the source of the randomness. However, because the question was soon closed (and rightly so) as a duplicate of a similar question, I decided to make a short post for the benefit of other people wondering the strange behaviour.

Designing personalized photo books is a great activity for dark winter evenings. One change introduced by digital photography is the number of snaps taken in every photo opportunity, and in total. Because sharing photos takes likewise less effort than in paper photo time, the photo book project could easily start with folders containing thousands of photos. However, not all the snaps are worth keeping.

As in information era in general, some smart person usually has already found a solution for the problem. A great post by Adrian Rosebrock describes how to quantify the blurriness in images using variation of the Laplacian. The continuous Laplacian is a well-known second-order differential operator and the discrete version of the operator (images are sets of pixels) has an application in edge detection. The main idea is that a sharp image should have a fair number of edges while unfocused image is more smooth.