我不知道是否有内置功能，但是手动操作相当简单
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
>>>
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