生成完整图形的代码未通过单元测试,但生成正确答案

以下代码在单元测试期间在标记有注释的行处产生此错误: (Exception: TypeError) "'int' object is not iterable"

可视化调试器不会检测到任何错误并生成所需的输出。也就是说,make\u complete\u graph(2)生成图{0:set([1]),1:set([0])}。

图形表示是不可协商的。

错误发生在突出显示的行上。置换例程包含在原始文件中,因为单元测试人员在导入itertools时遇到问题。然而,我在这里用itertools代替了简洁。如果您想知道为什么会发生这种情况,我们将不胜感激。

from itertools import permutations

def make_complete_graph(num_nodes):
    '''
    Input: Number of nodes (an int) in graph.
    Output: Complete directed graph containing all possible edges subject to restriction
    that self-loops are disallowed & number of nodes must be positive. If number of nodes is
    not positive, empty graph is returned. 
    '''
    if num_nodes > 0:
        new_dict = {}
        nodes = [i for i in range(0, num_nodes)]
        edges = list(permutations(nodes, r=2))
        for n in nodes:
            new_dict[n] = set()
            for e in edges:
                if n == e[0]:
                    # the error occurs at this line
                    new_dict[n].add(set(e[1]))
        return new_dict
    else:
        return {num_nodes: set([])}