from flask import Flask
 
app = Flask(__name__)
 
 
@app.route('/')
def hello_world():
    return 'Hello, world!'
 
if __name__ == '__main__':
    app.run(debug=True, host='0.0.0.0')

FROM python:3-onbuild
COPY . /usr/src/app
CMD ["python", "app.py"]

# Werkzeug==0.14.1
Flask

λ docker run flask_test
 * Serving Flask app "app" (lazy loading)
 * Environment: production
   WARNING: Do not use the development server in a production environment.
   Use a production WSGI server instead.
 * Debug mode: on
 * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
 * Restarting with stat
Traceback (most recent call last):
  File "app.py", line 11, in <module>
    app.run(debug=True, host='0.0.0.0')
  File "/usr/local/lib/python3.6/site-packages/flask/app.py", line 943, in run
    run_simple(host, port, self, **options)
  File "/usr/local/lib/python3.6/site-packages/werkzeug/serving.py", line 988, in run_simple
    run_with_reloader(inner, extra_files, reloader_interval, reloader_type)
  File "/usr/local/lib/python3.6/site-packages/werkzeug/_reloader.py", line 332, in run_with_reloader
    sys.exit(reloader.restart_with_reloader())
  File "/usr/local/lib/python3.6/site-packages/werkzeug/_reloader.py", line 176, in restart_with_reloader
    exit_code = subprocess.call(args, env=new_environ, close_fds=False)
  File "/usr/local/lib/python3.6/subprocess.py", line 267, in call
    with Popen(*popenargs, **kwargs) as p:
  File "/usr/local/lib/python3.6/subprocess.py", line 709, in __init__
    restore_signals, start_new_session)
  File "/usr/local/lib/python3.6/subprocess.py", line 1344, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
OSError: [Errno 8] Exec format error: '/usr/src/app/app.py