github_pagination_style.py

def _get_displayed_page_numbers(current, final):
    """
    This utility function determines a list of page numbers to display, based
    on the same pagination display style that GitHub use in their issue list pages.

    This gives us a nice contextually relevant set of page numbers to display.

    For example:
    current=14, final=16 -> [1, 2, None, 12, 13, 14, 15, 16]
    current=2, final=16 -> [1, 2, 3, 4, 5, None, 15, 16]
    current=8, final=16 -> [1, 2, None, 6, 7, 8, 9, 10, None, 15, 16]
    """
    assert current >= 1
    assert final >= current

    if final <= 8:
        return range(1, final + 1)

    # We always include the first two pages, last two pages, and
    # two pages either side of the current page.
    included = set((
        1, 2,
        current - 2, current - 1, current, current + 1, current + 2,
        final - 1, final
    ))

    # At the edges we include more page numbers.
    if current <= 6:
        included.add(3)
        included.add(4)
        included.add(5)
    if current >= final - 5:
        included.add(final - 2)
        included.add(final - 3)
        included.add(final - 4)

    # Now sort the page numbers and drop anything outside the limits.
    included = [
        idx for idx in sorted(list(included))
        if idx > 0 and idx <= final
    ]

    # Finally insert any `...` breaks
    if current > 6:
        included.insert(2, None)
    if current < final - 5:
        included.insert(len(included) - 2, None)
    return included