def span_trees(self):
"""
Span a tree for each battery with its houses.
For all nodes in the tree, determine all paths to
remaining houses and choose the cheapest path.
Add the new house to the tree and all nodes of
its path. Continue until all houses are in the tree.
"""
for battery in self.batteries:
mst = {}
tree = {battery: {}}
houses = copy.deepcopy(battery.houses)
for house in houses:
distance = get_distance(house, battery)
tree[battery][house] = distance
least_distance = {}
while houses:
for vertice in tree.keys():
distance_to_targets = tree[vertice]
house, distance = min(
distance_to_targets.items(), key=lambda x: x[1])
least_distance[vertice] = (house, distance)
link = min(least_distance.items(), key=lambda x: x[1][1])
from_vertice, new_vertice, distance = link[0], link[1][0], link[1][1]
new_nodes = pathfinder(from_vertice, new_vertice)[1:-1]
branch = Branch(from_vertice, new_vertice)
branch.load_path(new_nodes)
mst[branch] = distance
houses.remove(new_vertice)
for vertice in tree.keys():
del tree[vertice][new_vertice]
for node in new_nodes:
tree[node] = {}
for house in houses:
distance = get_distance(node, house)
tree[node][house] = distance
tree[new_vertice] = {}
for house in houses:
distance = get_distance(new_vertice, house)
tree[new_vertice][house] = distance
self.mst_container.append(mst)
