RuntimeError: dictionary changed size during iteration

[Ceesjan Luiten]

This bug report is identical to #21049 but for Django 1.7.

I run Django 1.7a2 with a Python3 virtualenv. Occasionally the runserver crashes with the following stacktrace:

System check identified no issues (0 silenced).
Traceback (most recent call last):
  File "manage.py", line 10, in <module>
    execute_from_command_line(sys.argv)
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/core/management/__init__.py", line 427, in execute_from_command_line
    utility.execute()
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/core/management/__init__.py", line 419, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/core/management/base.py", line 287, in run_from_argv
    self.execute(*args, **options.__dict__)
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/core/management/base.py", line 336, in execute
    output = self.handle(*args, **options)
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/core/management/commands/runserver.py", line 81, in handle
    self.run(*args, **options)
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/core/management/commands/runserver.py", line 90, in run
    autoreload.main(self.inner_run, args, options)
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/utils/autoreload.py", line 267, in main
    reloader(wrapped_main_func, args, kwargs)
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/utils/autoreload.py", line 233, in python_reloader
    reloader_thread()
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/utils/autoreload.py", line 212, in reloader_thread
    if fn():
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/utils/autoreload.py", line 139, in inotify_code_changed
    update_watch()
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/utils/autoreload.py", line 132, in update_watch
    for path in gen_filenames():
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/utils/autoreload.py", line 84, in gen_filenames
    filenames = [filename.__file__ for filename in sys.modules.values()
  File "/home/quinox/projecten/deadlines/virtual/lib/python3.3/site-packages/django/utils/autoreload.py", line 84, in <listcomp>
    filenames = [filename.__file__ for filename in sys.modules.values()
RuntimeError: dictionary changed size during iteration

The issue shows up sporadically, it can usually be triggered within 10 minutes by running the following command in a shell:

while true ; do touch project/xxx/models.py ; sleep 1s; done

The fix as suggested in #21049 seems to fix the issue, I haven't seen the runserver crash since I modified django/utils/autoreload.py lines 84-85 from:

filenames = [filename.__file__ for filename in sys.modules.values()
            if hasattr(filename, '__file__')]

to

filenames = [filename.__file__ for filename in list(sys.modules.values())
            if hasattr(filename, '__file__')]

[Claude Paroz]

Regression was introduced in 15f82c701161b327cef54b469c00b6cbe01534db.

[Claude Paroz <claude@…>]

In e0381cdf2e7f677c5b29f2e3351993e92915569a:

Fixed #22017 -- Prevented RuntimeError on Python 3

Refs #21049. Thanks quinox for the report.

[Alex Gaynor <alex.gaynor@…>]

In 608e6eb2959c6e56e5c702ca0d15fa0e6c2eef16:

Added an explanatory comment. Refs #22017