Breadth First Search (BFS) in Python

import queue


class BreadthFirstSearch:
    def __init__(self, graph):
        """
        graph: Graph represntation in the form of an adjecency list.
            E.g:  `B <- A -> C`, graph = { 'A' : ['B','C'], }
        """
        self._graph = graph

    def head(self):
        # NOTE: In Python 3.7.0 the insertion-order preservation nature of
        # dict objects has been declared to …