Question

想象一下，我有一个["a", "b", "c", "d"]

列表

我正在寻找一个Pythonic成语来做大致这个：

for first_elements in head(mylist):
   # would first yield ["a"], then ["a", "b], then ["a", "b", "c"]
   # until the whole list gets generated as a result, after which the generator
   # terminates.

我的感觉告诉我，这应该存在于内置，但它正在逃避我。怎么样你会这样做吗？

Answer 1

你是说这个？

def head(it):
    val = []
    for elem in it:
        val.append(elem)
        yield val

这需要任何可迭代的，而不仅仅是列表。

演示：

>>> for first_elements in head('abcd'):
...     print first_elements
... 
['a']
['a', 'b']
['a', 'b', 'c']
['a', 'b', 'c', 'd']

Answer 2

我可能会这样做：

def head(A) :
    for i in xrange(1,len(A)+1) :
        yield A[:i]

示例：

for x in head(["a", "b", "c", "d"]) :
    print x

['a']
['a', 'b']
['a', 'b', 'c']
['a', 'b', 'c', 'd']

在Python中迭代列表头的优雅方式

2 个答案: