Opened 5 years ago

Last modified 4 months ago

#15648 assigned New feature

Allow QuerySet.values_list() to return a namedtuple

Reported by: pbagwl Owned by: paulmillr
Component: Database layer (models, ORM) Version: master
Severity: Normal Keywords: namedtuple, tuple, queryset
Cc: kmike84@…, cg@…, dougal85@…, ShawnMilo, paulmillr@… Triage Stage: Accepted
Has patch: yes Needs documentation: yes
Needs tests: no Patch needs improvement: yes
Easy pickings: no UI/UX: no


Python 2.6 supports named tuples. Information about field names is stored in the tuple class, so there's no overhead like in dictionaries.
I propose to use them in querysets instead of values() / values_list().

qs = Items.objects.filter(...).namedtuples('title', 'amount', 'price')
for item in qs:
    print item.title, item.amount
    total += item.amount * item.price


from itertools import imap
from collections import namedtuple

# python 2.5 doesn't support named tuples, so we can use this

from django.db.models.query import ValuesQuerySet

class NamedTuplesQuerySet(ValuesQuerySet):
    def iterator(self):
        # get field names 
        extra_names = self.query.extra_select.keys()
        field_names = self.field_names
        aggregate_names = self.query.aggregate_select.keys()
        names = extra_names + field_names + aggregate_names
        # create named tuple class
        tuple_cls = namedtuple('%sTuple' % self.model.__name__, names)

        results_iter = self.query.get_compiler(self.db).results_iter()
        # wrap every string with our named tuple
        return imap(tuple_cls._make, results_iter)
from django.db.models.query import QuerySet

def namedtuples(self, *fields):
    return self._clone(klass=NamedTuplesQuerySet, setup=True, _fields=fields)
QuerySet.namedtuples = namedtuples

Attachments (2)

namedtuples.patch (11.2 KB) - added by Paul Miller <paulmillr@…> 4 years ago.
Named tuples patch
values_list_namedtuples.diff (5.1 KB) - added by akaariai 4 years ago.

Download all attachments as: .zip

Change History (21)

comment:1 Changed 5 years ago by kmike

  • Cc kmike84@… added
  • Needs documentation unset
  • Needs tests unset
  • Patch needs improvement unset

comment:2 follow-up: Changed 5 years ago by me@…

Why not



comment:3 in reply to: ↑ 2 Changed 5 years ago by pbagwl

Replying to me@…:

Why not



  1. repr(). values / values lists etc. are much easier to debug.
  2. deferred objects (only creates them) are not iterables

comment:4 Changed 5 years ago by adrian

  • Needs tests set
  • Patch needs improvement set
  • Triage Stage changed from Unreviewed to Accepted

I like the idea of introducing a QuerySet that returns named tuples! Not crazy about the name, but I can't think of a better one at the moment.

Can you create an actual .patch file, include unit tests and include a fallback namedtuple implementation for our Python 2.4/2.5 users? A good place for that would be in django/utils/

comment:5 Changed 5 years ago by lukeplant

  • Type set to New feature

comment:6 Changed 5 years ago by lukeplant

  • Severity set to Normal

comment:7 Changed 5 years ago by EnTeQuAk

  • Cc cg@… added

comment:8 Changed 5 years ago by d0ugal

  • Cc dougal85@… added
  • Easy pickings unset
  • Needs documentation set

comment:9 Changed 5 years ago by ShawnMilo

  • Cc ShawnMilo added

Changed 4 years ago by Paul Miller <paulmillr@…>

Named tuples patch

comment:10 Changed 4 years ago by Paul Miller <paulmillr@…>

  • Cc paulmillr@… added
  • Needs documentation unset
  • Needs tests unset
  • Patch needs improvement unset
  • UI/UX unset

I've added necessary tests and fallback implementation for Python 2.5 users.

comment:11 Changed 4 years ago by paulmillr

  • Owner changed from nobody to paulmillr
  • Status changed from new to assigned

comment:12 Changed 4 years ago by paulmillr

  • Triage Stage changed from Accepted to Ready for checkin

I don't know much about ticket triaging, but I think that «ready for checkin» would be more correct for this

comment:13 Changed 4 years ago by jezdez

  • Needs documentation set
  • Patch needs improvement set
  • Triage Stage changed from Ready for checkin to Accepted

This definitely isn't ready for checkin yet as there are no docs.

comment:14 Changed 4 years ago by jacob

  • milestone 1.4 deleted

Milestone 1.4 deleted

comment:15 Changed 4 years ago by akaariai

Why the namedtuples API? Is there some reason values_list should not return namedtuples directly? It should be backwards compatible, as index based fetching still work. I believe there will not be any serious performance impact.

If the performance is acceptable, then raw cursors should return named tuples, too. That would be a really nice addition for raw SQL users. But of course, this is another ticket's problem.

comment:16 Changed 4 years ago by akaariai

I have a very quick implementation of returning namedtuples from .values_list(). The patch seems to be backwards compatible, that is, all tests pass.

The performance penalty seems to be about 20% for one-field values_list() call. It is a good question if that is acceptable. I guess yes as namedtuples are _much_ nicer than regular tuples. On the other hand the main use case for values_list is performance.

The results are using SQLite to fetch 200 objects with one field containing a four char value, and then additional fields containing NULLs. values_list with one field gives the 20% performance penalty, 5 fields gives 15% penalty. Notably in-memory SQLite with fields containing practically no data is pretty much the worst-case. I guess the real-world penalty will be in 5%-20% range depending on use case. My opinion is that getting namedtuples is worth it.

I guess similar performance penalty would be paid if cursors were to return named tuples directly, and that is even tougher call to make. Cursors are even more performance critical, and every query made by Django would need to pay the penalty. Although when creating model instance for example that penalty would be hidden by overhead of model.__init__.

It is of course possible to add the .namedtuples() API, but then we have three things doing nearly the same thing, and two doing exactly the same thing from user perspective.

Changed 4 years ago by akaariai

comment:17 Changed 3 years ago by anonymous

This would be really, really nice.

comment:18 Changed 2 years ago by suprzer0@…

Perhaps adding a keyword argument to values_list() for namedtuples? something like

Item.objects.values_list(*names_list, named=True)

With named defaulting to False.

Calling .values_list(*names_list, named=True, flat=True) would need to throw some kind of exception I'd imagine.

comment:19 Changed 4 months ago by timgraham

  • Summary changed from [Feature request] NamedTupleQuerySet to Allow QuerySet.values_list() to return a namedtuple
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