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A few common issues are reported when trying to run Dallinger. Always run with the --verbose flag for full logs

Python Processes Kept Alive

Sometimes when trying to run experiments consecutively in Debug mode, a straggling process creates Server 500 errors. These are caused by background python processes and/or gunicorn workers. Filter for them using:

ps -ef | grep -E "python|gunicorn"

This will display all running processes that have the name python or gunicorn. To kill all of them, run these commands:

pkill python
pkill gunicorn

Known Postgres issues

If you get an error like the following...

createuser: could not connect to database postgres: could not connect to server:
    Is the server running locally and accepting
    connections on Unix domain socket "/tmp/.s.PGSQL.5432"?

...then you probably did not start the app.

If you get a fatal error that your ROLE does not exist, run these commands:

createuser dallinger
dropdb dallinger
createdb -O dallinger dallinger

Common Sandbox Error

❯❯ Launching the experiment on MTurk...

❯❯ Error parsing response from /launch, check web dyno logs for details: <!DOCTYPE html>
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <meta charset="utf-8">
        <title>Application Error</title>
        <style media="screen">
          html,body,iframe {
            margin: 0;
            padding: 0;
          html,body {
            height: 100%;
            overflow: hidden;
          iframe {
            width: 100%;
            height: 100%;
            border: 0;
        <iframe src="//"></iframe>
Traceback (most recent call last):
  File "/Users/user/.virtualenvs/dallinger/bin/dallinger", line 11, in <module>
    load_entry_point('dallinger', 'console_scripts', 'dallinger')()
  File "/Users/user/.virtualenvs/dallinger/lib/python3.6/site-packages/click/", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/Users/user/.virtualenvs/dallinger/lib/python3.6/site-packages/click/", line 697, in main
    rv = self.invoke(ctx)
  File "/Users/user/.virtualenvs/dallinger/lib/python3.6/site-packages/click/", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/user/.virtualenvs/dallinger/lib/python3.6/site-packages/click/", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/user/.virtualenvs/dallinger/lib/python3.6/site-packages/click/", line 535, in invoke
    return callback(*args, **kwargs)
  File "/Users/user/Dallinger/dallinger/", line 558, in sandbox
    _deploy_in_mode(u'sandbox', app, verbose)
  File "/Users/user/Dallinger/dallinger/", line 550, in _deploy_in_mode
    deploy_sandbox_shared_setup(verbose=verbose, app=app)
  File "/Users/user/Dallinger/dallinger/", line 518, in deploy_sandbox_shared_setup
    launch_data = _handle_launch_data('{}/launch'.format(heroku_app.url))
  File "/Users/user/Dallinger/dallinger/", line 386, in _handle_launch_data
    launch_data = launch_request.json()
  File "/Users/user/.virtualenvs/dallinger/lib/python3.6/site-packages/requests/", line 892, in json
    return complexjson.loads(self.text, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/", line 339, in loads
    return _default_decoder.decode(s)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/", line 364, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/", line 382, in raw_decode
    raise ValueError("No JSON object could be decoded")

If you get this from the sandbox, this usually means there's a deeper issue that requires dallinger logs --app XXXXXX. Usually this could be a requirements.txt file error (missing dependency or reference to an incorrect branch).

Combining Dallinger core development and running experiments

A common pitfall while doing development on the dallinger codebase while also working on external experiments which include dallinger as a dependency: you pip install a demo experiment in your active virtual environment, and it overwrites the dallinger.egg-link file in that environment's site-packages directory with an actual copy of the dallinger package.

When installing dallinger with the intent to work on dallinger, the recommended way to install dallinger itself is with pip's "editable mode", by passing the -e or --editable flag to pip install:

pip install -e .[data]

This creates a form of symbolic link in the active python's site-packages directory to the working copy of dallinger you're sitting in. This allows you to make changes to python files in the dallinger working copy and have them immediately active when using dallinger commands or any other actions that invoke the active python interpreter.

Running pip install without the -e flag, either while installing dallinger directly, or while installing a separate experiment which includes dallinger as a dependency, will instead place a copy of the dallinger package in the site-packages directory. These files will then be executed when the active python is running, and any changes to the files you're working on will be ignored.

You can check to see if you are working in "editable mode" by inspecting the contents of your active virtual environment's site-packages folder. In "editable mode", you will see a dallinger.egg-link file listed in the directory:

drwxr-xr-x    9 jesses  staff   306B May 29 12:30 coverage_pth-0.0.2.dist-info
-rw-r--r--    1 jesses  staff    44B May 29 12:30 coverage_pth.pth
-rw-r--r--    1 jesses  staff    33B Jun 14 16:08 dallinger.egg-link
drwxr-xr-x   21 jesses  staff   714B Mar 19 17:24 datashape
drwxr-xr-x   10 jesses  staff   340B Mar 19 17:24 datashape-0.5.2.dist-info

The contents of this file will include the path to the working copy that's active. If you instead see a directory tree with actual dallinger files, you can restore "editable mode" by re-running the installation steps for dallinger from the :doc:`developing_dallinger_setup_guide` documentation.