python - 查找子序列(非连续的)

Question

如果我有字符串 needle我想检查它是否作为 substring 在 haystack 中连续存在，我可以使用:

if needle in haystack:
    ...

在非连续子序列的情况下我可以使用什么？示例:

>>> haystack = "abcde12345"
>>> needle1 = "ace13"
>>> needle2 = "123abc"
>>> is_subsequence(needle1, haystack)
True
>>> is_subsequence(needle2, haystack)  # order is important!
False

Answer 1

不知道有没有自带的功能，手动操作还是比较简单的

def exists(a, b):
    """checks if b exists in a as a subsequence"""
    pos = 0
    for ch in a:
        if pos < len(b) and ch == b[pos]:
            pos += 1
    return pos == len(b)

>>> exists("moo", "mo")
True
>>> exists("moo", "oo")
True
>>> exists("moo", "ooo")
False
>>> exists("haystack", "hack")
True
>>> exists("haystack", "hach")
False
>>>