Test whether list A is contained in list B

Question

I have two lists, A & B, and I would like to test whether A is contained in B. By "contained" I mean that the elements of A appear in the exact same order within B with no other elements between them. What I'm looking for is very similar to the behavior of A in B if they were strings.

Some elements of A will be repeated. We can assume A will be shorter than B.

There are many answers to similar questions on SO, but most answer a different question:

• Is A an element of B? (Not my question: B is a flat list, not a list of lists.)
• Are all the elements of A contained in B? (Not my question: I'm concerned about order as well.)
• Is A a sublist of B? (Not my question: I don't want to know whether the elements of A appear in the same order in B, I want to know if they appear exactly as they are somewhere in B.)

If the operation were implemented as the keyword containedin, it would behave like this.

>>> [2, 3, 4] containedin [1, 2, 3, 4, 5]
True
>>> [2, 3, 4] containedin [1, 1, 2, 2, 3, 3, 4, 4, 5, 5]
False
>>> [2, 3, 4] containedin [5, 4, 3, 2, 1]
False
>>> [2, 2, 2] containedin [1, 2, 3, 4, 5]
False
>>> [2, 2, 2] containedin [1, 1, 2, 2, 3, 3, 4, 4, 5, 5]
False
>>> [2, 2, 2] containedin [1, 1, 1, 2, 2, 2, 3, 3, 3]
True

Is there a concise way to perform this operation in Python? Am I missing some important terminology that would have led me to the answer more quickly?

Answer 1

Use any with list slicing:

def contained_in(lst, sub):
    n = len(sub)
    return any(sub == lst[i:i+n] for i in range(len(lst)-n+1))

Or, use join to join both lists to strings and use in operator:

def contained_in(lst, sub):
    return ','.join(map(str, sub)) in ','.join(map(str, lst))

Usage:

>>> contained_in([1, 2, 3, 4, 5], [2, 3, 4])
True
>>> contained_in([1, 2, 2, 4, 5], [2, 3, 4])
False

Answer 2

many people have posted their answers. but I want to post my efforts anyway ;) this is my code:

def containedin(a,b):
    for j in range(len(b)-len(a)+1):
        if a==b[j:j+len(a)]:
            return True
    return False

print(containedin([2, 3, 4],[1, 2, 3, 4, 5]))
print(containedin([2, 3, 4],[1, 1, 2, 2, 3, 3, 4, 4, 5, 5]))
print(containedin([2, 3, 4],[5, 4, 3, 2, 1]))
print(containedin([2, 2, 2],[1, 2, 3, 4, 5]))
print(containedin([2, 2, 2],[1, 1, 1, 2, 2, 2, 3, 3, 3]))

this is the output: True False False False True