A few hours ago, when I was dealing with my thesis, I've come up with a Python function that constructs a tour for a given TSP instance using the nearest neighbor heuristic:
def nearestneighbor(size, dists):
tour = [0]*size
candy = [True]*size
candy[0] = False
for i in range(1, size):
prev = tour[i - 1]
tour[i] = min([(dists[prev][c], c)
for c in range(size) if candy[c] and c != prev])[1]