#26600: map says a queryset is not iterable
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Reporter: ihucos | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.8
Severity: Normal | Keywords: queryset
| iterator map
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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So I got a funny bug with iterators map and Django that I can not localize
or reproduce.
In our production server we get this sometimes, mainly for only one
customer and it only fails on a very small percentage of all requests.
Sorry for only chunks of information, not sure if it is enough to process
this bug request:
Th error message:
{{{
TypeError: argument 2 to map() must support iteration
}}}
Chunk of the code where this happens:
{{{#!python
if filter(
lambda obj:
self.pk in verbose_map(attrgetter('pk'),
obj.resources.all()) and
obj.begins < end and obj.ends > dt,
resource_override_qs):
return 0
}}}
Trying to reconstruct resource_override_qs I come up with:
{{{#!python
facility = Facility.objects.\
prefetch_related('resources',
'opening_hours',
'openinghour_overrides',
'slow_hours').\
get(pk=facility.pk)
resource_override_qs =
facility.facilityresourceoverride_set.prefetch_related('resources')
}}}
What I did was to replace map with verbose_map in our production
environment.
{{{#!python
def verbose_map(function, iterable):
try:
return map(function, iterable)
except TypeError, exc:
raise TypeError('map failed: "{}". iterable: {}, type: {}, attrs:
{}'.format( # NOQA
exc, iterable, type(iterable), dir(iterable)))
}}}
After two weeks or so the error occurred again:
{{{#!python
map failed: "argument 2 to map() must support iteration". iterable:
[<FacilityResource: 4>, <FacilityResource: 5>, <FacilityResource: 6>,
<FacilityResource: 7>], type: <class 'django.db.models.query.QuerySet'>,
attrs: ['__and__', '__bool__', '__class__', '__deepcopy__', '__delattr__',
'__dict__', '__doc__', '__format__', '__getattribute__', '__getitem__',
'__getstate__', '__hash__', '__init__', '__iter__', '__len__',
'__module__', '__new__', '__nonzero__', '__or__', '__reduce__',
'__reduce_ex__', '__repr__', '__setattr__', '__setstate__', '__sizeof__',
'__str__', '__subclasshook__', '__weakref__', '_add_hints', '_as_sql',
'_batched_insert', '_clone', '_create_object_from_params', '_db',
'_earliest_or_latest', '_extract_model_params', '_fetch_all',
'_filter_or_exclude', '_for_write', '_has_filters', '_hints', '_insert',
'_known_related_objects', '_merge_known_related_objects',
'_merge_sanity_check', '_next_is_sticky', '_populate_pk_values',
'_prefetch_done', '_prefetch_related_lookups',
'_prefetch_related_objects', '_prepare', '_raw_delete', '_result_cache',
'_setup_aggregate_query', '_sticky_filter', '_update', 'aggregate', 'all',
'annotate', 'as_manager', 'bulk_create', 'complex_filter', 'count',
'create', 'dates', 'datetimes', 'db', 'defer', 'delete', 'distinct',
'earliest', 'exclude', 'exists', 'extra', 'filter', 'first', 'get',
'get_or_create', 'in_bulk', 'is_compatible_query_object_type', 'iterator',
'last', 'latest', 'model', 'none', 'only', 'order_by', 'ordered',
'prefetch_related', 'query', 'raw', 'reverse', 'select_for_update',
'select_related', 'update', 'update_or_create', 'using',
'value_annotation', 'values', 'values_list']
}}}
As we can see map really gets an QuerySet object, that queryset object
does reveal its content in __str__ but python's built in map says its not
iterable nevertheless
Alone for the customer where this happens the most that part of the code
should be called at least a couple of times per day.
I am going with a workaround like calling list() on the queryset before
mapping it or so.
But my company should be ok, to try this again with another verbose_map
that may provide more debugging information. My efforts to reproduce this
in our code base failed.
--
Ticket URL: <https://code.djangoproject.com/ticket/26600>
Django <https://code.djangoproject.com/>
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