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Version 23 (modified by programmerq, 6 years ago) (diff)

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Better Error Messages

Good error messages make for more productive developers. This page is a place to collect error messages that could stand improvement, or which are misleading or confusing in certain contexts. Most of us have had the experience of getting a "weird" message, puzzling it out (perhaps with help from django-users or #django) and then moving on.

Some of these may seem like quick patches but others will take a bit of consideration -- that's why the wiki page rather than individual tickets. Some are more along the lines of "Django Lint" than simple changes to error output.

For now, let's try dividing them into sections by major module. Within those sections suggested format is: error message, explanatory context (often important -- a message that is very helpful in one context can be confusing in another), suggested improvements/changes.

Also see:

django.contrib.admin

'NoneType' object has no attribute 'get_field_sets'

Context: One or more models that are referenced by ForeignKey from another model are missing their inner Admin class. Possible other causes as well. See ticket #1808.
Suggestion: Check relevant Admin settings during model validation?

  • Ticket #3219 -- suggestion for better error messages for invalid Admin attributes

django.core

TypeError at ...
string indices must be integers

Context: A FileUploadField is being validated but the form did not have enctype="multipart/form-data" set.
Suggestion: Check form enctype during validation? Show FILES in addition to GET and POST on error pages?

  • Ticket #3221 -- patch for better error message for faulty URLconf
  File "c:\django\django\core\urlresolvers.py", line 255, in _get_urlconf_module
    raise ImproperlyConfigured, "Error while importing URLconf %r: %s" % (self.urlconf_name, e)

ImproperlyConfigured: Error while importing URLconf 'reports.urls': tuple index out of range

Context: A Trying to load my home page and it is evidently finding something wrong with my urls.py
Suggestion: Output which tuple it is trying to index, and perhaps even the entire 'patterns'

  • Ticket #6537 -- Unhelpful error message: 'tuple index out of range'

django.core.servers

AttributeError: WSGIRequestHandler instance has no attribute 'path'

Context: This error gets raised when a server started by runserver is (by accident) accessed via https://. Details here.
Suggestion: runserver does not support https, please use it only via http.

django.db

OperationalError: Unable to close due to unfinalised statements

Context: SQLite file permissions are incorrect (directory or DB file lack write permission)
Suggestion: Check file permissions when running with SQLite backend and warn user if they seem incorrect

ProgrammingError: ERROR:  current transaction is aborted, commands ignored until end of transaction block

This pyscopg2 (PostgreSQL) error usually signifies that some previous database query was incorrect (e.g., you tried to order_by() a field that doesn't exist, or put a string in an integer column, etc.). That previous error aborted the transaction, causing all subsequent database access to fail with this message.

If you get this while at a shell, you can fix your database connection by executing a rollback:

from django.db import connection
connection.cursor().execute('rollback')

If you get this from a view, it probably means the immediately previous query had a problem (but was caught by an over-eager exception handler).

In certain situations with PostgreSQL, a bogus error message about SET TIME ZONE may be returned. See #3179 (which is closed, but has a description of the problem). The real error message can probably be found in the postgres log file.

django.http

AttributeError: Http404 instance has no attribute 'has_header'

Context: Http404 is returned instead of raised
Suggestion: Check type of HttpResponse before attempting to use (perhaps unPythonic?) or possibly give Http404 a clearer name like Http404Exception

django.template

django.template.__init__.py

Using an invalid template tag results in the generic 'list index out of range' error which doesn't show any information about the offending file or expression. E.g., if a template contains:

...
{% invalid_template_tag %} 
...

An error occurs at line 279 of django.template.__init__.py:

278   try:
279      compiled_result = compile_func(self, token)
280   except KeyError:
281      self.invalid_block_tag(token, command)
282   except TemplateSyntaxError, e:
283      if not self.compile_function_error(token,e):
291          raise

What seems to be happening is that self.invalid_block_tag(...) raises an error which gets caught by TemplateSyntaxError and which eventually leads to the generic 'list index out of range' error being reported in the Django error page.

FIXED

  • Ticket #1732 -- a problem that elicits no error message, but should.