class Author(models.Model):
    title = CharField()

class Genre(models.Model):
    title = CharField()

class Book(models.Model):
    title = CharField()
    author = ManyToManyField(Author)
    genre = ManyToManyField(Genre)

if request.POST:
    book_list = Book.objects.all() #get all books from db
    books = []

    request_list = request.POST.getlist('genre') #select list of genres in request
        for item in request_list:
            add_book = report_list.filter(genre=r_request) #queryset of book filtered by each genre
            books.append(add_book)
            book_list = book_list.exclude(genre=item)

    request_list = request.POST.getlist('author') #select list of authors in request
        for item in request_list:
            add_book = report_list.filter(author=item) #queryset of book filtered by each author
            books.append(add_book)
            book_list = book_list.exclude(author=item)
    return ...
        'books': books

genre_list= request.POST.getlist('genre')
author_list = request.POST.getlist('author')
books = Book.objects.filter(genre__in=genre_list,author__in=author_list)

from django.db.models import Q
genre_list= request.POST.getlist('genre')
author_list = request.POST.getlist('author')
books = Book.objects.filter(Q(genre__in=genre_list) | Q(author__in=author_list))

genre_list= request.POST.getlist('genre')
author_list = request.POST.getlist('author')

query = None

if gender_list:
    gender_q = Q(genre__in=genre_list)
    query = gender_q

if author_list:
    author_q = Q(author__in=author_list)
    if gender_list:
       query|=author_q
    else:
       query = author_q

books = []
if query:
   books = Book.objects.filter(query).distinct()