Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.11
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  wontfix
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Abhijeet):

 I'm unsure if bumping this up is against forum rules. However, I get this
 Error in Py3k in production. I'm not using `map` in my code, though I'm
 unsure if Django is internally using it.

 This is the code block that produces the error. The save method is
 overriding the save method of a Mode called `Transaction`.
 {{{
 def save(self, *args, **kwargs):
 obj = self
 if not obj.ref_number:  # Set the reference number before saving
 transactions = Transaction.objects.values_list("ref_number",
 flat=True) # cache the list
 while True:
 ref_number = random.randint(11, 99)
 if ref_number not in transactions:
 obj.ref_number = ref_number
 super(Transaction, obj).save(*args, **kwargs)
 return
 else:
 super(Transaction, obj).save(*args, **kwargs)
 }}}

 The erroring line of code is:  `if ref_number not in transactions:`
 This piece of code was working fine until we had modified another
 unrelated part of the source code.

 {{{
 items =
 
OrderItem.objects.prefetch_related('toppings').select_related('item').select_related('item__category')
 order = Order.objects.filter(uuid=order_uuid).prefetch_related(
 Prefetch(
 lookup='items',
 queryset=items
 )
 
).select_related('outlet').select_related('user').select_related('outlet__group')
 \
  .select_for_update(of=('self', 'outlet'))
 }}}

 What we did was add the call to `select_for_update`, followed by a
 transaction which modifies the `Order` and `Outlet` model. Here, the
 `Order` model is a child model of the `Transaction` model.

 My guess as to what the problem is is that `select_for_update` locks the
 relevant rows/table which results in the line of code in the `save` method
 to fail internally, ultimately being caught as a cryptic type error. I'll
 be modifying
 `transactions = Transaction.objects.values_list("ref_number", flat=True)`
 to
 `transactions = Transaction.objects.values_list("ref_number",
 flat=True).list()` to see if that'll fix the problem.

 PS: I'm sorry if my formatting/post/bump is against norms. I'm new here,
 with this being my first comment.

 Replying to [comment:8 Simon Charette]:
 > I think we can close as ''wontfix'' given `map` doesn't turn
 `__iter__()` exceptions into `TypeError` on Py3k and we don't support Py2k
 anymore.
 >
 > Thanks for the investigation Vitaliy.

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Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.11
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  wontfix
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Philipp Kuznetsov):

 I'm really sorry, of course in case of `in` exception message is `argument
 of type 'QuerySet' is not iterable`. This has nothing to do with `map` and
 ofc there's an obvious workaround with `exists()`. What I am afraid of is
 if there are more of this hidden cases where queryset's `__iter__` raises
 an exception and it's shadowed by the outer code exception.

 Replying to [comment:11 Simon Charette]:
 > Philipp, if you hit a similar exception that means `map` must be
 involved somehow.
 >
 > If you didn't call it yourself then it's likely caused by a usage of
 `map` internally in the queryset iteration code.
 >
 > In this case the ticket resolution still stands, Python 2 `map`'s
 shadowing of the underlying exception makes it impossible to determine its
 true nature and thus we cannot conclude Django is at fault. As mentioned
 previously this should all be solved on Python 3 where `map` doesn't
 exhibit this behaviour.
 >
 > By the way an `in` operation on a queryset you are disposing off is
 likely to trigger a `MemoryError` just like in the original report. I'd
 suggest you opt for something along
 `queryset.filter(pk=instance.pk).exists()` instead.

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Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.11
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  wontfix
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Simon Charette):

 Philipp, if you hit a similar exception that means `map` must be involved
 somehow.

 If you didn't call it yourself then it's likely caused by a usage of `map`
 internally in the queryset iteration code.

 In this case the ticket resolution still stands, Python 2 `map`'s
 shadowing of the underlying exception makes it impossible to determine its
 true nature and thus we cannot conclude Django is at fault. As mentioned
 previously this should all be solved on Python 3 where `map` doesn't
 exhibit this behaviour.

 By the way an `in` operation on a queryset you are disposing off is likely
 to trigger a `MemoryError` just like in the original report. I'd suggest
 you opt for something along `queryset.filter(pk=instance.pk).exists()`
 instead.

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Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.11
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  wontfix
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by pro100filipp):

 The problem is not only with the map. We faced the same issue when using
 code like this:

 {{{
 if model_instance in model.objects.all():
 ...
 }}}

 Replying to [comment:8 Simon Charette]:
 > I think we can close as ''wontfix'' given `map` doesn't turn
 `__iter__()` exceptions into `TypeError` on Py3k and we don't support Py2k
 anymore.
 >
 > Thanks for the investigation Vitaliy.

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Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.11
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  wontfix
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Vitaliy):

 There are at least two ways to workaround the error on Py2k:
 *  force the queryset into a list when using `map`
 * use `imap` (from `itertools`) instead of `map`

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Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.11
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  wontfix
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Simon Charette):

 * status:  new => closed
 * resolution:   => wontfix


Comment:

 I think we can close as ''wontfix'' given `map` doesn't turn `__iter__()`
 exceptions into `TypeError` on Py3k and we don't support Py2k anymore.

 Thanks for the investigation Vitaliy.

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Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  new
Component:  Database layer   |  Version:  1.11
  (models, ORM)  |
 Severity:  Normal   |   Resolution:
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Carlton Gibson):

 * status:  closed => new
 * resolution:  needsinfo =>


Comment:

 I'm going to reopen so we review the reproduce.

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Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.11
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Vitaliy):

 * version:  1.8 => 1.11


Comment:

 I found a way to reproduce the error.

 Class **A** is a simplified version of **QuerySet**
 {{{#!python
 class A(object):

 def __init__(self):
 self._result_cache = None

 def _fetch_all(self):
 if self._result_cache is None:
 self._result_cache = list(self.iterator())

 def iterator(self):
 for x in range(10):
 if x == 5:
 raise MemoryError  # the type of exception doesn't matter
 yield x

 def __iter__(self):
 self._fetch_all()
 return iter(self._result_cache)
 }}}

 {{{#!python
 In [2]: map(str, A())
 ---
 TypeError Traceback (most recent call
 last)
 /home/user/workspace/project/service/models.pyc in ()
 > 1 map(str, A())

 TypeError: argument 2 to map() must support iteration
 }}}

 When using python 3:
 {{{#!python
 In [6]: map(str, A())
 ---
 MemoryError   Traceback (most recent call
 last)
  in ()
 > 1 map(str, A())

  in __iter__(self)
  15
  16 def __iter__(self):
 ---> 17 self._fetch_all()
  18 return iter(self._result_cache)
  19

  in _fetch_all(self)
   6 def _fetch_all(self):
   7 if self._result_cache is None:
 > 8 self._result_cache = list(self.iterator())
   9
  10 def iterator(self):

  in iterator(self)
  11 for x in range(10):
  12 if x == 5:
 ---> 13 raise MemoryError
  14 yield x
  15

 MemoryError:
 }}}

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Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.8
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by Sergey Fedoseev):

 * cc: Sergey Fedoseev (added)


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Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.8
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by Brian Hahn):

 I am also seeing this issue, and have to force the queryset into a list to
 workaround this error. Any plausible idea why this might be happening?

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Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.8
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by ihucos):

 We got where it comes from.
 This exception occurs after Heroku times out the request, but apparently
 it does not kill it: https://devcenter.heroku.com/articles/request-timeout

 So this happens in some funny Heroku environment that I really can't
 reproduce.

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Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.8
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-

Comment (by shaib):

 FWIW, the original traceback (which your `verbose_map()` hides) may be
 much more informative. Guessing that you're on Python 2,  you may want to
 rewrite it as something like:

 {{{#!python
 def verbose_map(function, iterable):
 try:
 return map(function, iterable)
 except TypeError:
 e_cls, e_inst, traceback = sys.exc_info()
 raise TypeError, (
'map failed: "{}". iterable: {}, type: {}, attrs:
 {}'.
format(e_inst, iterable, type(iterable),
 dir(iterable))
   ), traceback
 }}}

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Re: [Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
-+-
 Reporter:  ihucos   |Owner:  nobody
 Type:  Bug  |   Status:  closed
Component:  Database layer   |  Version:  1.8
  (models, ORM)  |
 Severity:  Normal   |   Resolution:  needsinfo
 Keywords:  queryset iterator| Triage Stage:
  map|  Unreviewed
Has patch:  0|  Needs documentation:  0
  Needs tests:  0|  Patch needs improvement:  0
Easy pickings:  0|UI/UX:  0
-+-
Changes (by timgraham):

 * status:  new => closed
 * needs_better_patch:   => 0
 * resolution:   => needsinfo
 * needs_tests:   => 0
 * needs_docs:   => 0


Comment:

 No, I can't figure out if or where a bug might in Django based on the
 report.

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[Django] #26600: map says a queryset is not iterable

[Django]

#26600: map says a queryset is not iterable
--+
 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
--+
 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:
 [, , ,
 ], type: ,
 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: 
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