Dictionaries in Python

Question

What do these two statements mean in Python?

distances[(clust[i].id,clust[j].id)]=distance(clust[i].vec,clust[j].vec)

d=distances[(clust[i].id,clust[j].id)]

I am guessing that the first statement assigns clust[i].id and clust[j].id keys of the distances map to the result of the distance(..) function. However, I am confused since lists are represented using [] and dictionaries using {} in Python. What's the correct answer?

Answer 1

distances[(clust[i].id,clust[j].id)]=distance(clust[i].vec,clust[j].vec)

distances is a dictionary where keys are tuples of probably integers and the value is the distance measured between them by the distance function. in the second line:

d=distances[(clust[i].id,clust[j].id)]

the d variable is just assigned to that distance, accessing the dictionary value just assigned. other answers provide the summary of what's a dictionary.

Answer 2

Hopefully this will make it clear:

>>> a = {}
>>> a[1] = 2
>>> a[(1, 2)] = 3
>>> a
{(1, 2): 3, 1: 2}

Answer 3

Dictionary literals use {}. Indexing operations use [], regardless of type.