Check if a Page object is associated with the given tag.

    :param page: a Page instance
    :param tag: a Tag instance or a slug string.

    :return: whether the Page instance has the given tag attached (False if no Page or no
             attached PageTags exists)
    :type: Boolean

def page_has_tag(page, tag):
    """
    Check if a Page object is associated with the given tag.

    :param page: a Page instance
    :param tag: a Tag instance or a slug string.

    :return: whether the Page instance has the given tag attached (False if no Page or no
             attached PageTags exists)
    :type: Boolean
    """
    from .models import PageTags
    if hasattr(tag, 'slug'):
        slug = tag.slug
    else:
        slug = tag
    try:
        return page.pagetags.tags.filter(slug=slug).exists()
    except PageTags.DoesNotExist:
        return False