helper.py

class PaginationHelper:

    # The constructor takes in an array of items and a integer indicating
    # how many items fit within a single page
    def __init__(self, collection, items_per_page):
        self.collection = collection
        self.items_per_page = items_per_page

    # returns the number of items within the entire collection
    def item_count(self):
        return len(self.collection)

    # returns the number of pages
    def page_count(self):
        return len(self.collection) // self.items_per_page + 1

    # returns the number of items on the current page. page_index is zero based
    # this method should return -1 for page_index values that are out of range
    def page_item_count(self, page_index):
        if page_index > len(self.collection) // self.items_per_page or page_index < 0:
            return -1
        else:
            return len(self.collection[self.items_per_page * page_index:self.items_per_page * (page_index + 1)])

    # determines what page an item is on. Zero based indexes.
    # this method should return -1 for item_index values that are out of range
    def page_index(self, item_index):
        if item_index not in range(len(self.collection)):
            return -1
        else:
            return len(self.collection[:item_index]) // self.items_per_page

collection = range(1,25)
helper = PaginationHelper(collection, 10)

print(helper.page_count())     #, 3, 'page_count is returning incorrect value.')
print(helper.page_index(23))   #, 2, 'page_index returned incorrect value')
print(helper.item_count())  #, 24, 'item_count returned incorrect value')
print(helper.page_item_count(2))