Plotly Dash 应用程序未运行

Question

我正在尝试从 jupyter notebook 运行以下代码：

import dash
import dash_core_components as dcc
import dash_html_components as html

external_stylesheets = ['https://codepen.io/chriddyp/pen/bWLwgP.css']

app = dash.Dash(__name__, external_stylesheets=external_stylesheets)

app.layout = html.Div(children=[
    html.H1(children='Hello Dash'),

    html.Div(children='''
        Dash: A web application framework for Python.
    '''),

    dcc.Graph(
        id='example-graph',
        figure={
            'data': [
                {'x': [1, 2, 3], 'y': [4, 1, 2], 'type': 'bar', 'name': 'SF'},
                {'x': [1, 2, 3], 'y': [2, 4, 5], 'type': 'bar', 'name': u'Montréal'},
            ],
            'layout': {
                'title': 'Dash Data Visualization'
            }
        }
    )
])

if __name__ == '__main__':
    app.run_server(debug=True)

它产生以下内容：

 * Serving Flask app "__main__" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on
 * Running on http://127.0.0.1:8050/ (Press CTRL+C to quit)
 * Restarting with stat
An exception has occurred, use %tb to see the full traceback.

SystemExit: 1


//anaconda3/lib/python3.7/site-packages/IPython/core/interactiveshell.py:3333: UserWarning:

To exit: use 'exit', 'quit', or Ctrl-D.

当我点击http://127.0.0.1:8050/ 时，页面永远不会加载。我已经尝试了一段时间了。回复中是否有我遗漏的内容？这应该是一个基本的破折号应用程序。

这是回溯：

---------------------------------------------------------------------------
SystemExit                                Traceback (most recent call last)
<ipython-input-1-b057c246c3cf> in <module>
     29 
     30 if __name__ == '__main__':
---> 31     app.run_server(debug=True)
     32 
     33 get_ipython().run_line_magic('tb', '')

//anaconda3/lib/python3.7/site-packages/dash/dash.py in run_server(self, port, debug, **flask_run_options)
    566                    debug=False,
    567                    **flask_run_options):
--> 568         self.server.run(port=port, debug=debug, **flask_run_options)

//anaconda3/lib/python3.7/site-packages/flask/app.py in run(self, host, port, debug, load_dotenv, **options)
    988 
    989         try:
--> 990             run_simple(host, port, self, **options)
    991         finally:
    992             # reset the first request information if the development server

//anaconda3/lib/python3.7/site-packages/werkzeug/serving.py in run_simple(hostname, port, application, use_reloader, use_debugger, use_evalex, extra_files, reloader_interval, reloader_type, threaded, processes, request_handler, static_files, passthrough_errors, ssl_context)
   1005         from ._reloader import run_with_reloader
   1006 
-> 1007         run_with_reloader(inner, extra_files, reloader_interval, reloader_type)
   1008     else:
   1009         inner()

//anaconda3/lib/python3.7/site-packages/werkzeug/_reloader.py in run_with_reloader(main_func, extra_files, interval, reloader_type)
    330             reloader.run()
    331         else:
--> 332             sys.exit(reloader.restart_with_reloader())
    333     except KeyboardInterrupt:
    334         pass

SystemExit: 1

Answer 1

开箱即用，如上一个答案所述，您不能运行 debug=True。因此人们坚持：

在 jupyter 上，执行以下操作：

if __name__ == '__main__':
    app.run_server()

在 VSCode 等编辑器上，您可以执行以下操作：

if __name__ == '__main__':
    app.run_server(debug=True)

您仍然热衷于使用 Jupyter 而不是代码编辑器？
该问题的讨论始于这个已解决的Github 问题；在 plotly中突出显示了禁用调试的需要；讨论催生了jupyter-dash作为解决方案。

问题在于：
启用调试模式直接启用重载器。反过来，重新加载器会导致任何 Flask 应用程序在启动时被初始化两次，这是 Jupyter 无法应对的。事实上，你甚至可以在 jupyter 中运行 debug=True ，前提是你禁用了重新加载器。

因此，您可以这样做：

if __name__ == '__main__':
    app.run_server(debug=True, use_reloader=False)

Answer 2

您无法在 jupyter 笔记本上以调试模式运行 dash，您必须禁用调试模式或转向良好的老式文本编辑器/IDE：

if __name__ == '__main__':
    app.run_server(debug=False)