Determination of singlesource shortestpath. This BellmanFord Code is for determination whether we can get shortest path from given graph or not for singlesource shortestpaths problem. In other words, if given graph has any negativeweight cycle that is reachable from the source, then it will give answer False for no solution exits. For argument graph, it should be a dictionary type such as graph   'a': 'b': 6, 'e': 7, 'b': 'c': 5, 'd': 4, 'e': 8, 'c': 'b': 2, 'd': 'a': 2, 'c': 7, 'e': 'b': 3  Initialize data structures for BellmanFord algorithm.
def bellman_ford(graph, source):
    """
    This Bellman-Ford Code is for determination whether we can get
    shortest path from given graph or not for single-source shortest-paths problem.
    In other words, if given graph has any negative-weight cycle that is reachable
    from the source, then it will give answer False for "no solution exits".
    For argument graph, it should be a dictionary type
    such as
    graph = {
        'a': {'b': 6, 'e': 7},
        'b': {'c': 5, 'd': -4, 'e': 8},
        'c': {'b': -2},
        'd': {'a': 2, 'c': 7},
        'e': {'b': -3}
    }
    """
    weight = {}
    pre_node = {}

    initialize_single_source(graph, source, weight, pre_node)

    for _ in range(1, len(graph)):
        for node in graph:
            for adjacent in graph[node]:
                if weight[adjacent] > weight[node] + graph[node][adjacent]:
                    weight[adjacent] = weight[node] + graph[node][adjacent]
                    pre_node[adjacent] = node

    for node in graph:
        for adjacent in graph[node]:
            if weight[adjacent] > weight[node] + graph[node][adjacent]:
                return False

    return True

def initialize_single_source(graph, source, weight, pre_node):
    """
    Initialize data structures for Bellman-Ford algorithm.
    """
    for node in graph:
        weight[node] = float('inf')
        pre_node[node] = None

    weight[source] = 0
