python列表理解按步骤2

Question

xlabels = ["first", "second", "third", "fourth"]

是否有办法在2之前完成一份清单的理解？

for i in range(0,len(xlabels)):
    xlabels[i]=""

变成["" for i in xlabels]

它会把列表变成空白。输出：["","","",""]

怎么了？：

for i in range(0,len(xlabels),2):
    xlabels[i]=""

我想把列表中的每一项都变成空白。输出：["", "second", "", "fourth"]

Answer 1

通过使用带有step的range()，您就在正确的轨道上了。列表理解倾向于创建一个新列表，而不是修改现有的列表。但是，您仍然可以执行以下操作：

>>> xlabels = [1, 2, 3, 4]
>>> [xlabels[i] if i % 2 != 0 else '' for i in range(len(xlabels))]
['', 2, '', 4]

Answer 2

就我个人而言，我会将列表切片和列表理解结合在一起：

>>> full_list = ['first', 'second', 'third', 'fourth', 'fifth']
>>> [element for element in full_list[::2]]
['first', 'third', 'fifth']

Answer 3

除非您需要更广泛的内容，否则您也可以这样做：

>>> xlabels = ["first", "second", "third", "fourth"]
>>> [i%2 * label for i, label in enumerate(xlabels)]
['', 'second', '', 'fourth']