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.