+def async_build_pdf(book_id, customizations, file_name):
+ """
+ A celery task to generate pdf files.
+ Accepts the same args as Book.build_pdf, but with book id as first parameter
+ instead of Book instance
+ """
+ try:
+ book = catalogue.models.Book.objects.get(id=book_id)
+ print "will gen %s" % DefaultStorage().path(file_name)
+ if not DefaultStorage().exists(file_name):
+ book.build_pdf(customizations=customizations, file_name=file_name)
+ print "done."
+ except Exception, e:
+ print "Error during pdf creation: %s" % e
+ print_exc
+ raise e
+
+
+class MultiQuerySet(object):
+ def __init__(self, *args, **kwargs):
+ self.querysets = args
+ self._count = None
+
+ def count(self):
+ if not self._count:
+ self._count = sum(len(qs) for qs in self.querysets)
+ return self._count
+
+ def __len__(self):
+ return self.count()
+
+ def __getitem__(self, item):
+ try:
+ indices = (offset, stop, step) = item.indices(self.count())
+ except AttributeError:
+ # it's not a slice - make it one
+ return self[item : item + 1][0]
+ items = []
+ total_len = stop - offset
+ for qs in self.querysets:
+ if len(qs) < offset:
+ offset -= len(qs)
+ else:
+ items += list(qs[offset:stop])
+ if len(items) >= total_len:
+ return items
+ else:
+ offset = 0
+ stop = total_len - len(items)
+ continue