More efficient BFS

bfs.py

# OLD
from collections import deque

queue = deque(starting_values)
while queue:
      item = queue.popleft()
      queue.extend(item.children)
      # ... do things with item ...
      
# Less alloc
from itertools import chain

queue = [starting_values]
for item in chain.from_iterable(queue):
      queue.append(item.children)
      # ... do things with item ...
      
# Only allocating a pointer to our iterator location, and only adding to the list one item for each set of children. 30x faster