RuntimeError when running ./manage.py runserver

[lvella@…]

This happened to me when I tried to "./manage.py runserver":

$ ./manage.py runserver
Validating models...

Traceback (most recent call last):
  File "./manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/home/vella/projetos/chroni9/venv/site-packages/django/core/management/__init__.py", line 397, in execute_from_command_line
    utility.execute()
  File "/home/vella/projetos/chroni9/venv/site-packages/django/core/management/__init__.py", line 390, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/vella/projetos/chroni9/venv/site-packages/django/core/management/base.py", line 240, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/home/vella/projetos/chroni9/venv/site-packages/django/core/management/base.py", line 283, in execute
    output = self.handle(*args, **options)
  File "/home/vella/projetos/chroni9/venv/site-packages/django/core/management/commands/runserver.py", line 75, in handle
    self.run(*args, **options)
  File "/home/vella/projetos/chroni9/venv/site-packages/django/core/management/commands/runserver.py", line 84, in run
    autoreload.main(self.inner_run, args, options)
  File "/home/vella/projetos/chroni9/venv/site-packages/django/utils/autoreload.py", line 181, in main
    reloader(wrapped_main_func, args, kwargs)
  File "/home/vella/projetos/chroni9/venv/site-packages/django/utils/autoreload.py", line 148, in python_reloader
    reloader_thread()
  File "/home/vella/projetos/chroni9/venv/site-packages/django/utils/autoreload.py", line 129, in reloader_thread
    if code_changed():
  File "/home/vella/projetos/chroni9/venv/site-packages/django/utils/autoreload.py", line 60, in code_changed
    for m in sys.modules.values():
RuntimeError: dictionary changed size during iteration

I am using Django 1.6b2, with the totally experimental Python 3 implementation from PyPy 2.1, so I can not be sure if this really is a Django Python 3 issue, just PyPy issue, or PyPy Python 3 issue.

It happened only once, just now, and I was unable to reproduce. I am using SQLite, if that matters...

[Claude Paroz]

Right, in Python 3 values() returns a dictionary view (​http://docs.python.org/3/library/stdtypes.html#dictionary-view-objects), not a copy of the values as in Python 2. Probably wrapping sys.modules.values() inside list() would be sufficient to ensure thread-safety.

[mburst]

The pull request for this ticket is here ​https://github.com/django/django/pull/1575

[Max Burstein <mburst@…>]

In 559cb826b850faeb7ad198a3a78a38f07dcf3b42:

Fixed #21049 -- Fixed autoreload for Python 3

Changed th system module values check to return a list.
In Python 3 it returns a dict_view which could occassionally produce
a runtime error of "dictionary changed size during iteration".

[Andrew Godwin <andrew@…>]

In ce5e09353d4ac3bda10f95e1cc8e609b0b397fdc:

Merge pull request #1575 from mburst/ticket_21049

Fixed #21049 -- Fixed autoreload for Python 3

[Tim Graham <timograham@…>]

In 92e89452f1aa3987cb70648e69718c6adea4b079:

[1.6.x] Fixed #21049 -- Fixed autoreload for Python 3

Changed th system module values check to return a list.
In Python 3 it returns a dict_view which could occassionally produce
a runtime error of "dictionary changed size during iteration".

Backport of 559cb826b8 from master

[Claude Paroz <claude@…>]

In e0381cdf2e7f677c5b29f2e3351993e92915569a:

Fixed #22017 -- Prevented RuntimeError on Python 3

Refs #21049. Thanks quinox for the report.