运行多个具有服务布局功能的 Dash 应用程序

Question

我目前正在尝试运行多个具有服务布局功能的 Plotly Dash 应用程序（请参阅下面的代码以及 serve_layout1() 和 serve_layout2() 功能）。我需要它们，因为我必须在布局中包含几个全局变量，这样当有人在浏览器中单击刷新按钮时，我的应用程序就会更新。多个 Dash 应用程序在没有服务布局功能的情况下也能正常工作。但是，当我尝试运行多个具有服务布局功能的应用程序时，事情开始出错。

这是我的文件结构：

- app.py
- index.py
- apps
   |-- __init__.py
   |-- app1.py
   |-- app2.py

其中app.py:

import dash
app = dash.Dash(__name__, suppress_callback_exceptions=True)
server = app.server

index.py:

import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output

from app import app
from apps import app1, app2

from apps.app1 import serve_layout1
from apps.app2 import serve_layout2

app.layout = html.Div([
    dcc.Location(id='url', refresh=False),
    html.Div(id='page-content')
])


@app.callback(Output('page-content', 'children'),
              Input('url', 'pathname'))
def display_page(pathname):
    if pathname == '/apps/app1':
        app1.layout = serve_layout1
        return app1.layout
    elif pathname == '/apps/app2':
        app2.layout = serve_layout2
        return app2.layout
    else:
        return '404'

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

app1.py:

import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output
from app import app

def serve_layout1():

    global df

    # uploading cvs as dataframe, doing some computation here and etc (skipped)

    app_layout1 = html.Div([
        html.H3('App 1'),
        dcc.Dropdown(
            id='app-1-dropdown',
            options=[
                {'label': 'App 1 - {}'.format(i), 'value': i} for i in [
                    'NYC', 'MTL', 'LA'
                ]
            ]
        ),
        html.Div(id='app-1-display-value'),
        dcc.Link('Go to App 2', href='/apps/app2')
    ])

    return app_layout1

@app.callback(
    Output('app-1-display-value', 'children'),
    Input('app-1-dropdown', 'value'))
def display_value(value):
    return 'You have selected "{}"'.format(value)

app2.py:

import dash_core_components as dcc
import dash_html_components as html
from dash.dependencies import Input, Output
from app import app

def serve_layout2():

    global df

    # uploading cvs as dataframe, doing some computation here and etc (skipped)

    app_layout2 = html.Div([
        html.H3('App 2'),
        dcc.Dropdown(
            id='app-2-dropdown',
            options=[
                {'label': 'App 2 - {}'.format(i), 'value': i} for i in [
                    'NYC', 'MTL', 'LA'
                ]
            ]
        ),
        html.Div(id='app-2-display-value'),
        dcc.Link('Go to App 2', href='/apps/app1')
    ])


    return app_layout2


@app.callback(
    Output('app-1-display-value', 'children'),
    Input('app-1-dropdown', 'value'))
def display_value(value):
    return 'You have selected "{}"'.format(value)

当我运行应用程序时，出现以下错误：

Traceback (most recent call last):
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\site-packages\dash\dash.py", line 1039, in add_context
    response, cls=plotly.utils.PlotlyJSONEncoder
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\json\__init__.py", line 238, in dumps
    **kw).encode(obj)
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\site-packages\_plotly_utils\utils.py", line 45, in encode
    encoded_o = super(PlotlyJSONEncoder, self).encode(o)
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\json\encoder.py", line 199, in encode
    chunks = self.iterencode(o, _one_shot=True)
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\json\encoder.py", line 257, in iterencode
    return _iterencode(o, 0)
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\site-packages\_plotly_utils\utils.py", line 115, in default
    return _json.JSONEncoder.default(self, obj)
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\json\encoder.py", line 180, in default
    o.__class__.__name__)
TypeError: Object of type 'function' is not JSON serializable

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\site-packages\flask\app.py", line 1950, in full_dispatch_request
    rv = self.dispatch_request()
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\site-packages\flask\app.py", line 1936, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\site-packages\dash\dash.py", line 1072, in dispatch
    response.set_data(func(*args, outputs_list=outputs_list))
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\site-packages\dash\dash.py", line 1042, in add_context
    _validate.fail_callback_output(output_value, output)
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\site-packages\dash\_validate.py", line 256, in fail_callback_output
    _validate_value(val, index=i)
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\site-packages\dash\_validate.py", line 251, in _validate_value
    toplevel=True,
  File "C:\Users\iakubal\Anaconda3\envs\general_3_6\lib\site-packages\dash\_validate.py", line 205, in _raise_invalid
    bad_val=bad_val,
dash.exceptions.InvalidCallbackReturnValue: The callback for `<Output `page-content.children`>`
returned a value having type `function`
which is not JSON serializable.


The value in question is either the only value returned,
or is in the top level of the returned list,

and has string representation
`<function serve_layout1 at 0x0000016B49DABB70>`

In general, Dash properties can only be
dash components, strings, dictionaries, numbers, None,
or lists of those.

Answer 1

问题是您没有在此处调用 serve_layout 函数：

@app.callback(Output("page-content", "children"), Input("url", "pathname"))
def display_page(pathname):
    if pathname == "/apps/app1":
        app1.layout = serve_layout1
        return app1.layout
    elif pathname == "/apps/app2":
        app2.layout = serve_layout2
        return app2.layout
    else:
        return "404"

你应该这样做：

@app.callback(Output("page-content", "children"), Input("url", "pathname"))
def display_page(pathname):
    if pathname == "/apps/app1":
        app1.layout = serve_layout1()
        return app1.layout
    elif pathname == "/apps/app2":
        app2.layout = serve_layout2()
        return app2.layout
    else:
        return "404"

因此，您返回的是对函数的引用，而不是函数的破折号组件 returns。

这无效，因为您分享的错误消息是这样说的：

In general, Dash properties can only be dash components, strings, dictionaries, numbers, None, or lists of those.

同样在 app2.py 中，您在回调中引用了错误的 ID。您正在为 app1.py 引用 ids。您不能有重复的回调输出。所以 app2.py 中的回调应该是这样的：

@app.callback(
    Output("app-2-display-value", "children"), Input("app-2-dropdown", "value")
)
def display_value(value):
    return 'You have selected "{}"'.format(value)

运行多个具有服务布局功能的 Dash 应用程序

Run multiple Dash apps with serve layout functions

python

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plotly-dash

运行 多个具有服务布局功能的 Dash 应用程序

Run multiple Dash apps with serve layout functions

python

global-variables

dataframe

plotly

plotly-dash

运行多个具有服务布局功能的 Dash 应用程序