unsupported operand type(s) for +: 'NoneType' and 'str'

lkerzuah · May 30, 2024, 5:50pm

Environment:


Request Method: GET
Request URL: http://localhost:8000/admin/stockmgmgt/stock/

Django Version: 5.0.6
Python Version: 3.12.3
Installed Applications:
['stockmgmgt',
 'crispy_forms',
 'django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']


Template error:
In template C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\contrib\admin\templates\admin\change_list.html, error at line 68
   unsupported operand type(s) for +: 'NoneType' and 'str'
   58 :         {% block search %}{% search_form cl %}{% endblock %}
   59 :         {% block date_hierarchy %}{% if cl.date_hierarchy %}{% date_hierarchy cl %}{% endif %}{% endblock %}
   60 : 
   61 :         <form id="changelist-form" method="post"{% if cl.formset and cl.formset.is_multipart %} enctype="multipart/form-data"{% endif %} novalidate>{% csrf_token %}
   62 :         {% if cl.formset %}
   63 :           <div>{{ cl.formset.management_form }}</div>
   64 :         {% endif %}
   65 : 
   66 :         {% block result_list %}
   67 :           {% if action_form and actions_on_top and cl.show_admin_actions %}{% admin_actions %}{% endif %}
   68 :            {% result_list cl %} 
   69 :           {% if action_form and actions_on_bottom and cl.show_admin_actions %}{% admin_actions %}{% endif %}
   70 :         {% endblock %}
   71 :         {% block pagination %}{% pagination cl %}{% endblock %}
   72 :         </form>
   73 :       </div>
   74 :       {% block filters %}
   75 :         {% if cl.has_filters %}
   76 :           <div id="changelist-filter">
   77 :             <h2>{% translate 'Filter' %}</h2>
   78 :             {% if cl.is_facets_optional or cl.has_active_filters %}<div id="changelist-filter-extra-actions">


Traceback (most recent call last):
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\db\models\options.py", line 681, in get_field
    return self.fields_map[field_name]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^

During handling of the above exception ('action_checkbox'), another exception occurred:
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\contrib\admin\utils.py", line 289, in lookup_field
    f = _get_non_gfk_field(opts, name)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\contrib\admin\utils.py", line 322, in _get_non_gfk_field
    field = opts.get_field(name)
            ^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\db\models\options.py", line 683, in get_field
    raise FieldDoesNotExist(
    ^

During handling of the above exception (Stock has no field named 'action_checkbox'), another exception occurred:
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\core\handlers\exception.py", line 55, in inner
    response = get_response(request)
               ^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\core\handlers\base.py", line 220, in _get_response
    response = response.render()
               ^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\response.py", line 114, in render
    self.content = self.rendered_content
                   ^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\response.py", line 92, in rendered_content
    return template.render(context, self._request)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\backends\django.py", line 61, in render
    return self.template.render(context)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 171, in render
    return self._render(context)
           ^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 163, in _render
    return self.nodelist.render(context)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 1000, in render
    return SafeString("".join([node.render_annotated(context) for node in self]))
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 961, in render_annotated
    return self.render(context)
           ^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\loader_tags.py", line 159, in render
    return compiled_parent._render(context)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 163, in _render
    return self.nodelist.render(context)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 1000, in render
    return SafeString("".join([node.render_annotated(context) for node in self]))
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 961, in render_annotated
    return self.render(context)
           ^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\loader_tags.py", line 159, in render
    return compiled_parent._render(context)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 163, in _render
    return self.nodelist.render(context)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 1000, in render
    return SafeString("".join([node.render_annotated(context) for node in self]))
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 961, in render_annotated
    return self.render(context)
           ^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\loader_tags.py", line 65, in render
    result = block.nodelist.render(context)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 1000, in render
    return SafeString("".join([node.render_annotated(context) for node in self]))
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 961, in render_annotated
    return self.render(context)
           ^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\loader_tags.py", line 65, in render
    result = block.nodelist.render(context)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 1000, in render
    return SafeString("".join([node.render_annotated(context) for node in self]))
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\base.py", line 961, in render_annotated
    return self.render(context)
           ^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\contrib\admin\templatetags\base.py", line 45, in render
    return super().render(context)
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\template\library.py", line 258, in render
    _dict = self.func(*resolved_args, **resolved_kwargs)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\contrib\admin\templatetags\admin_list.py", line 345, in result_list
    "results": list(results(cl)),
               ^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\contrib\admin\templatetags\admin_list.py", line 321, in results
    yield ResultList(None, items_for_result(cl, res, None))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\contrib\admin\templatetags\admin_list.py", line 312, in __init__
    super().__init__(*items)
    ^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\contrib\admin\templatetags\admin_list.py", line 217, in items_for_result
    f, attr, value = lookup_field(field_name, result, cl.model_admin)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\contrib\admin\utils.py", line 298, in lookup_field
    value = attr(obj)
            ^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\contrib\admin\options.py", line 999, in action_checkbox
    "aria-label": format_html(_("Select this object for an action - {}"), obj),
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\utils\html.py", line 135, in format_html
    return mark_safe(format_string.format(*args_safe, **kwargs_safe))
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\utils\html.py", line 117, in conditional_escape
    return escape(text)
           ^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\utils\functional.py", line 231, in wrapper
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\varte\AppData\Local\Programs\Python\Python312\Lib\site-packages\django\utils\html.py", line 50, in escape
    return SafeString(html.escape(str(text)))
                                  ^^^^^^^^^
  File "C:\Users\varte\OneDrive\Desktop\Projects\Stock Mangement\venv\src\stockmgmgt\models.py", line 25, in __str__
    return self.item_name+' '+str(self.quantity)
           ^^^^^^^^^^^^^^^^^^

Exception Type: TypeError at /admin/stockmgmgt/stock/
Exception Value: unsupported operand type(s) for +: 'NoneType' and 'str'

KenWhitesell · May 31, 2024, 3:36am

Side note: When posting code (or templates, error messages, tracebacks, etc), enclose the code between lines of three backtick - ` characters. This means you’ll have a line of ```, then your code, then another line of ```. This forces the forum software to keep your code properly formatted. (I’ve taken the liberty of editing your original post. Please remember to do this in the future.)

KenWhitesell · May 31, 2024, 3:39am

This is saying that self.item_name is null for the model being rendered.

lkerzuah · May 31, 2024, 9:03am

So, How do you resolve this error please?

KenWhitesell · May 31, 2024, 1:20pm

To even begin to try to offer a suggestion, we’d need to see the model.

lkerzuah · May 31, 2024, 1:33pm

Thanks for you always relying to my post. I have resolve this error. I used this code def str(self):
return f"{self.item_name} {self.quantity}"

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