python - 理解 - 从字典字段中列出

Question

目前，我正在这样做:

nodes = set([relation.source for relation in relations] +
            [relation.target for relation in relations])

肯定有更简单的方法，但我找不到。

有点像

nodes = set([(relation.source, relation.target) for relation in relations])

但这当然行不通。谢谢

[编辑]忘了说:relations 是一个字典，或者在我的例子中，是一个对象的集合。

Answer 1

您可以在 *-comprehension(列表、集合、字典、生成器表达式)中使用多个 for 子句:

nodes = {
    x
    for relation in relations
    for x in [relation.source, relation.target]
}

上面的表达式类似于:

nodes = set()
for relation in relations:
    for x in [relation.source, relation.target]:
        nodes.add(x)
nodes

---

使用生成函数的替代方法:

def source_targets(relations):
    for relation in relations:
        yield relation.source
        yield relation.target

nodes = set(source_targets(relations))