jython 2.7b2 and flask reload - subprocess issue

gistfile1.txt

# hello.py
from flask import Flask
app = Flask(__name__)
 
@app.route('/')
def hello_world():
    return "Hellox, World!"
 
    if __name__ == '__main__':
        app.debug = True # <------ removing this everything works fine
        app.run()



(venv)paolo@tk:$ java -jar jython-standalone-2.7-b2.jar app/hello.py 
 * Running on http://127.0.0.1:5000/
 * Restarting with reloader
Traceback (most recent call last):
  File "app/hello.py", line 10, in <module>
    app.run()
  File "/home/paolo/jdevel/golap-workspace/venv/project/Lib/flask/app.py", line 772, in run
    run_simple(host, port, self, **options)
  File "/home/paolo/jdevel/golap-workspace/venv/project/Lib/werkzeug/serving.py", line 708, in run_simple
    run_with_reloader(inner, extra_files, reloader_interval)
  File "/home/paolo/jdevel/golap-workspace/venv/project/Lib/werkzeug/serving.py", line 617, in run_with_reloader
    sys.exit(restart_with_reloader())
  File "/home/paolo/jdevel/golap-workspace/venv/project/Lib/werkzeug/serving.py", line 617, in run_with_reloader
    sys.exit(restart_with_reloader())
  File "/home/paolo/jdevel/golap-workspace/venv/project/Lib/werkzeug/serving.py", line 601, in restart_with_reloader
    exit_code = subprocess.call(args, env=new_environ)
  File "/home/paolo/jdevel/golap-workspace/venv/project/jython-standalone-2.7-b2.jar/Lib/subprocess.py", line 500, in call
  File "/home/paolo/jdevel/golap-workspace/venv/project/jython-standalone-2.7-b2.jar/Lib/subprocess.py", line 830, in __init__
  File "/home/paolo/jdevel/golap-workspace/venv/project/jython-standalone-2.7-b2.jar/Lib/subprocess.py", line 1309, in _execute_child
TypeError: args must contain only strings

When using Jython standalone package sys.executable is None - which causes the failure above.
Disabling the reloader resolves the issue ie: app.run(use_reloader=False)

Download the installer from http://mvnrepository.com/artifact/org.python/jython-installer and use this Jython instead of standalone. This should fix the issue. If it's not possible, a workaround proposed on #jython (freenode) to make the standalone version work, is adding shell=True to subprocess.call from serving.py in werkzeug and set args[0] to the script name.

Created a workaround for the standalone here: https://github.com/transistor1/werkzeug, using paolodina's serving.py method. Checks if the platform is Jython before using. Seems to work on both Linux and Windows, though not tested extensively. You can just replace your serving.py file with this one https://github.com/transistor1/werkzeug/blob/master/werkzeug/serving.py

Note you also need to add -Dpython.cachedir.skip=false to your Java command line, or Jython won't be able to find java.lang.management:

java -Dpython.cachedir.skip=false -jar /path/to/jython/jarfile.jar flask_file_to_run.py