Seeing if a list exists within another list?

Question

Basically lets say i have:

>>> a = [1,3,2,2,2]
>>> b = [1,3,2]

I want to see if the all the elements in b, exists within a, and in the same order. So for the above example b would exist within a.

I am kinda hoping theres a really simple one line answer.

Answer 1

This is a simple O(n * m) algorithm:

any(a[i:i + len(b)] == b for i in range(len(a) - len(b) + 1))

Note that is not the fastest way of doing this. If you need high performance you could use similar techniques to those used in string searching algorithms.

Answer 2

If by 'in the same order' you meant subsequence (as opposed to substring) then this non-one-liner should work fast:

  def is_subsequence(x, y):
    i, j = 0, 0
    while i < len(x) and j < len(y):
      if x[i] == y[j]:
        i += 1
      j += 1
    return i == len(x)