Return a topologically sorted list of nodes from a graph represented by an adjacency array dictionary

def topologicalSort(graph):
    visited = []
    stack = []

    for v in graph:
        if v not in visited:
            topologicalSortUtil(v, graph, visited, stack)

    return stack


def topologicalSortUtil(curr, graph, visited, stack):
    visited.append(curr)

    for v in graph[curr]:
        if v not in visited:
            topologicalSortUtil(v, graph, visited, stack)

    stack.insert(0, curr)

graph = {
    'a': ['b', 'c', 'd'],
    'b': ['e'],
    'c': ['e'],
    'd': ['e'],
    'e': []
}

print(topologicalSort(graph))