我想知道是否有一条快捷方式可以在Python列表中列出一个简单的列表.
我可以在for循环中做到这一点,但也许有一些很酷的"单行"？我用reduce尝试了,但是我收到了一个错误.
码
l = [[1, 2, 3], [4, 5, 6], [7], [8, 9]]
reduce(lambda x, y: x.extend(y), l)
错误信息
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 1, in <lambda>
AttributeError: 'NoneType' object has no attribute 'extend'
我理解这一点没有问题:
a = [1,2,3,4]
b = [x for x in a]
我以为就是这样,但后来我找到了这个片段:
a = [[1,2],[3,4],[5,6]]
b = [x for xs in a for x in xs]
这使得b = [1,2,3,4,5,6].问题是我在理解语法方面遇到了麻烦[x for xs in a for x in xs],有人能解释一下它是如何工作的吗？