How to check if an element from List A is not present in List B in Python?

if the items in the list are hashable:

>>> set(A) - set(B)
{1, 2, 3}

otherwise, you may use filter function:

>>> list(filter(lambda a: a not in B, A))
[1, 2, 3]

in that case, if B is sorted, you may get a better performance by using bisect.bisect_left to search logarithmically:

>>> def pred(a):  # if B is already *sorted*
...     from bisect import bisect_left
...     i = bisect_left(B, a)
...     return i == len(B) or B[i] != a
... 
>>> list(filter(pred, A))
[1, 2, 3]

You can also use list comprehension:

C=[i for i in A if i not in B]

Output:

[1, 2, 3]

Using list comprehension:

truthy answer

any([True for x in [1, 2, 3, 4] if x in [4, 5, 6, 7]])

list of elements not present in the second list

[x for x in [1, 2, 3, 4] if x not in [4, 5, 6, 7]]

That's a typical case for boolean operations on sets:

zerotonine = set(range(10))
fourtoten = set(range(4,11))
print "exclusively in one:", zerotonine ^ fourtoten
exclusively in one: set([0, 1, 2, 3, 10])