NaN can be stored in DecimalField but cannot be retrieved

[dennisvang]

Description

If, for whatever reason, a NaN value (either float('nan'), math.nan, or numpy.nan) is stored in a DecimalField using sqlite3, the object cannot be retrieved from the database.

Attempts to do so will raise TypeError: argument must be int or float

This issue also breaks e.g. the admin changelist view.

Steps to reproduce

1. Create a brand new project using python 3.8.10 and django 3.2.6 with the default sqlite3 backend (optionally with numpy 1.21.2).

2. Create a model with a DecimalField:

class MyModel(models.Model):
    value = models.DecimalField(max_digits=10, decimal_places=5)

3. Programmatically create a model instance with value=float('nan') (or math.nan, or numpy.nan), then try to retrieve the object from the database (or refresh from database).

obj = MyModel.objects.create(value=float('nan'))
# the following raises a "TypeError: argument must be int or float"
obj.refresh_from_db()  

4. Visiting the admin changelist view for the model will also raise the error.

Traceback:

Internal Server Error: /nanbug/mymodel/1/change/
Traceback (most recent call last):
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/contrib/admin/options.py", line 616, in wrapper
    return self.admin_site.admin_view(view)(*args, **kwargs)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/utils/decorators.py", line 130, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/views/decorators/cache.py", line 44, in _wrapped_view_func
    response = view_func(request, *args, **kwargs)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/contrib/admin/sites.py", line 232, in inner
    return view(request, *args, **kwargs)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/contrib/admin/options.py", line 1660, in change_view
    return self.changeform_view(request, object_id, form_url, extra_context)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/utils/decorators.py", line 43, in _wrapper
    return bound_method(*args, **kwargs)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/utils/decorators.py", line 130, in _wrapped_view
    response = view_func(request, *args, **kwargs)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/contrib/admin/options.py", line 1540, in changeform_view
    return self._changeform_view(request, object_id, form_url, extra_context)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/contrib/admin/options.py", line 1561, in _changeform_view
    obj = self.get_object(request, unquote(object_id), to_field)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/contrib/admin/options.py", line 763, in get_object
    return queryset.get(**{field.name: object_id})
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/db/models/query.py", line 431, in get
    num = len(clone)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/db/models/query.py", line 262, in __len__
    self._fetch_all()
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/db/models/query.py", line 1324, in _fetch_all
    self._result_cache = list(self._iterable_class(self))
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/db/models/query.py", line 68, in __iter__
    for row in compiler.results_iter(results):
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/db/models/sql/compiler.py", line 1122, in apply_converters
    value = converter(value, expression, connection)
  File "/home/.../.local/share/virtualenvs/howto-GW7qAAiJ/lib/python3.8/site-packages/django/db/backends/sqlite3/operations.py", line 313, in converter
    return create_decimal(value).quantize(quantize_value, context=expression.output_field.context)
TypeError: argument must be int or float