def annotate(self, *args, **kwargs):
        annotations = OrderedDict()  # To preserve ordering of args
        for arg in args:
            # The default_alias property may raise a TypeError, so we use
            # a try/except construct rather than hasattr in order to remain
            # consistent between PY2 and PY3 (hasattr would swallow
            # the TypeError on PY2).
            try:
                if arg.default_alias in kwargs:
                    raise ValueError("The named annotation '%s' conflicts with the "
                                     "default name for another annotation."
                                     % arg.default_alias)
            except (AttributeError, TypeError):
                raise TypeError("Complex annotations require an alias")
            annotations[arg.default_alias] = arg
        annotations.update(kwargs)

        clone = self._clone()
        names = self._fields
        if names is None:
            names = {f.name for f in self.model._meta.get_fields()}

        for alias, annotation in annotations.items():
            if alias in names:
                raise ValueError("The annotation '%s' conflicts with a field on "
                                 "the model." % alias)
            clone.query.add_annotation(annotation, alias, is_summary=False)

        for alias, annotation in clone.query.annotations.items():
            if alias in annotations and annotation.contains_aggregate:
                if clone._fields is None:
                    clone.query.group_by = True
                else:
                    clone.query.set_group_by()
                break

        return clone
Return a query set in which the returned objects have been annotated
dataset/ETHPy150Open django/django/django/db/models/query.py/QuerySet.annotate