The sequence protocol requires that items can be retrieved using square brackets with an integer index:

item = sequence[index]

The items can be searched for with index():

i = sequence.index(item)

The items can be counted with count():

num = sequence.count(item)

They can be a reversed copy of the sequence can be produced with reversed():

r = reversed(sequence)

In addition, the sequence protocol requires that the object support the iterable, sized, and containers.