获取包含特定项目的所有可能列表切片

Question

我试图找到包含特定项目的所有列表切片。假设我有一个由五个语素组成的列表w，其中一个是词stem，我想找到包含它的每个可能的切片。这是我为此写的代码：

stem = 'stm'
w = ['a', 'b', stem, 'c', 'd']
w2 = w
stem_index = w.index(stem)
stem_slice1 = w[stem_index:]
stem_slice2 = w[:stem_index + 1]
slices = []

while len(w) > 0:
    w = w[:-1] # chops the last item
    if stem in w and w not in slices:
        slices.append(w)

    w_ = w[1:] # then chops the first item
    if stem in w_ and w_ not in slices:
        slices.append(w_)

    w2 = w2[1:] # chops the first item
    if stem in w2 and w2 not in slices:
        slices.append(w2)

    w2_ = w2[:-1] # then chops the last item
    if stem in w2_ and w2_ not in slices:
        slices.append(w2_)

while len(stem_slice1) > 0:
    stem_slice1 = stem_slice1[:-1]
    if stem in stem_slice1 and stem_slice1 not in slices:
        slices.append(stem_slice1)

while len(stem_slice2) > 0:
    stem_slice2 = stem_slice2[1:]
    if stem in stem_slice2 and stem_slice2 not in slices:
        slices.append(stem_slice2)

print (slices)

运行时，此代码打印：

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

它似乎工作正常，但我想知道是否有更多的Pythonic方式来做同样的事情。

Answer 1

只需获得所有有效开始和结束指数的笛卡尔积即可。换句话说，两个for循环就足够了。

stem = 'stm'
w = ['a', 'b', stem, 'c', 'd']
idx = w.index(stem)
slices = []
for start in range(idx+1):
    for end in range(idx+1, len(w)+1):
        slices.append(w[start:end])
print(slices)

结果：

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