练习 - 帮助调试嵌套列表理解

Question

我有一本字典，如：

output = {'all_paths': [{'path': [{'to': '59v4aQo015zRyeGZ', 'proximity': 6, 'from': '4Po9aW3oxoNaAQzW'}], 'weight': 6}, {'path': [{'to': '59v4aQo015zRyeGZ', 'proximity': 7, 'from': 'AyD8rYemY6er47Vk'}, {'to': 'ZGmDayG795LRojPv', 'proximity': 6, 'from': 'AyD8rYemY6er47Vk'}, {'to': '59v4aQo015zRyeGZ', 'proximity': 6, 'from': '4Po9aW3oxoNaAQzW'}, {'to': 'ZGmDayG795LRojPv', 'proximity': 6, 'from': '4Po9aW3oxoNaAQzW'}, {'to': '59v4aQo015zRyeGZ', 'proximity': 6, 'from': 'eEo7aB0vgkdRO02V'}, {'to': 'ZGmDayG795LRojPv', 'proximity': 4, 'from': 'eEo7aB0vgkdRO02V'}], 'weight': 35}, {'path': [{'to': 'LWbARpjEjpZae3DZ', 'proximity': 4, 'from': '4Po9aW3oxoNaAQzW'}, {'to': '59v4aQo015zRyeGZ', 'proximity': 6, 'from': '4Po9aW3oxoNaAQzW'}], 'weight': 10}, {'path': [{'to': 'ZGmDayG795LRojPv', 'proximity': 6, 'from': '4Po9aW3oxoNaAQzW'}], 'weight': 6}, {'path': [{'to': 'LWbARpjEjpZae3DZ', 'proximity': 4, 'from': '4Po9aW3oxoNaAQzW'}], 'weight': 4}, {'path': [{'to': 'ZGmDayG795LRojPv', 'proximity': 7, 'from': 'LWbARpjEjpZae3DZ'}], 'weight': 7}]}

我想创建两个集合，一个包含字段“to”中的所有 id，另一个包含字段“from”中的所有 id。

为了简洁起见，我尝试了列表理解，但得到了一个意想不到的结果，只包含一个主题：

nf = set([edge['from'] for edge in path['path'] for path in output['all_paths']])

# set(['LWbARpjEjpZae3DZ'])

正确的结果是：

nf = set()

for edge in [path['path'] for path in output['all_paths']]:

    nf.add( edge[0]['from'])

# set(['AyD8rYemY6er47Vk', '4Po9aW3oxoNaAQzW', 'LWbARpjEjpZae3DZ'])

你能帮助指出我的嵌套列表理解有什么问题吗？

Answer 1

您可以使用嵌套理解：d = {i.get('from', i.get('id')) for b in output['all_paths'] for i in b['path']}输出：{'LWbARpjEjpZae3DZ', 'eEo7aB0vgkdRO02V', 'AyD8rYemY6er47Vk', '4Po9aW3oxoNaAQzW'}