为什么Dash上传文件时会出现解析错误? [英] Why is Dash giving a parse error when uploading files?

问题描述

上传Excel或CSV会导致错误.我遵循了Dash演示，但是一旦我尝试对其进行扩展以进行诸如绘图之类的操作时，它将无法正常工作.我不想只显示一张桌子. Dash_Table函数已更新，因此以前使用Dash_Table_Experiments的示例不再起作用

Uploading Excel or CSV results in an error. I followed the Dash demo, but as soon as I try to extend it to do something like plotting, it doesn't work. I don't want to just show a table. The Dash_Table function was updated, so previous examples that used Dash_Table_Experiments no longer work

我整夜都在交换堆栈，修改代码和阅读其他解决方案.完整的工作代码如下.我还想添加一个下拉回调函数，以通过分类变量过滤"数据.

I've spent the whole night on stack exchange, tinkering with my code and reading other solutions. the full working code is provided below. I'd like to also add a drop down call back function to "filter" the data by a categorical variable.

 import base64
 import datetime
 import io
 import plotly.graph_objs as go
 import dash
 from dash.dependencies import Input, Output, State
 import dash_core_components as dcc
 import dash_html_components as html
 import dash_table

 import pandas as pd


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

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

 app.layout = html.Div([
  dcc.Upload(
      id='upload-data',
      children=html.Div([
        'Drag and Drop or ',
        html.A('Select Files')
    ]),
    style={
        'width': '100%',
        'height': '60px',
        'lineHeight': '60px',
        'borderWidth': '1px',
        'borderStyle': 'dashed',
        'borderRadius': '5px',
        'textAlign': 'center',
        'margin': '10px'
    },
    # Allow multiple files to be uploaded
    multiple=False
  ),
  html.Div(id='output-data-upload'),
  dcc.Graph(id='graph1')
 ])


 def parse_contents(contents, filename):
   content_type, content_string = contents.split(',')

   decoded = base64.b64decode(content_string)

   try:
       if 'csv' in filename:
         # Assume that the user uploaded a CSV file
          df = pd.read_csv(
            io.StringIO(decoded.decode('utf-8')))
       elif 'xls' in filename:
          # Assume that the user uploaded an excel file
          df = pd.read_excel(io.BytesIO(decoded))
   except Exception as e:
       print(e)
       return html.Div([
           'There was an error processing this file.'
       ])

return html.Div([
    html.H5(filename),
    # html.H6(datetime.datetime.fromtimestamp(date)),

    dash_table.DataTable(
        data=df.to_dict('records'),
        columns=[{'name': i, 'id': i} for i in df.columns]
    ),

    html.Hr(),  # horizontal line
    # For debugging, display the raw contents provided by the web browser
    html.Div('Raw Content'),
    html.Pre(contents[0:200] + '...', style={
        'whiteSpace': 'pre-wrap',
        'wordBreak': 'break-all'
    })
 ])


 @app.callback(Output('output-data-upload', 'children'),
          [Input('upload-data', 'contents')],
          [State('upload-data', 'filename')])
 def update_output(list_of_contents, list_of_names):
   if list_of_contents is not None:
       children = [
           parse_contents(c, n) for c, n in
           zip(list_of_contents, list_of_names)]
      return children

@app.callback(
   Output('graph1', 'figure'),
   [Input('upload-data', 'contents'),
   Input('upload-data', 'filename')])

def plot_graph(contents, filename):
   df = parse_contents(contents, filename)
   trace1 = go.Bar(
        x=df['Quarter'],
        y=df['Score'],
    )

layout = go.Layout(
    title='graph1'

)
fig = go.Figure(data = [trace1], layout=layout)
return fig

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

我得到的错误是:更新output-data-upload.children的回调错误:ValueError:没有足够的值要解包(预期2，得到1)

The error I get is: Callback error updating output-data-upload.children: ValueError: not enough values to unpack (expected 2, got 1)

和

AttributeError:'NoneType'对象没有属性'split'

AttributeError: 'NoneType' object has no attribute 'split'

问题似乎出在python处理解析器的方式上:

The problem appears to be with how python is handling the parser:

  def parse_contents(contents, filename):
     content_type, content_string = contents.split(',')

   decoded = base64.b64decode(content_string)

但是，所有解决方案似乎都无法解决问题.

But none of the solutions seem to resolve the problem.

请帮助.既然有这么多人在为此苦苦挣扎(看来)，那么如果我们能够解决它并发布一个能完成Shiny可以轻松完成的功能的代码(Github?)，那就太好了.

please help. Since so many people are struggling with this (it would seem), it would be great if we could resolve it and post a functioning code (Github?) that accomplishes what Shiny can so easily do already.

推荐答案

您的代码:

   children = [
       parse_contents(c, n) for c, n in
       zip(list_of_contents, list_of_names)]

然后

def parse_contents(contents, filename):
    content_type, content_string = contents.split(',')
    decoded = base64.b64decode(content_string)
    ...

在c在无"中出现错误时，则parse_contents的contents参数为无"，并且发生无无.split"错误.

Here the error happens when c in None, then the contents parameter of parse_contents is None, and the "None has no .split" error happens.

如果c不是None而是只有一个单词，则contents.split()仅返回一个元素，并且发生没有足够的值要解压"错误.

If c is not None but only has one word, then contents.split() returns just one element, and the "not enough values to unpack" error happens.

我将对其进行过滤:

pairs = zip(list_of_contents, list_of_names)
children = [parse_contents(c, n) for (c, n) in pairs if c and (len(c.split(',')) == 2)]

您还可以考虑在parse_contents外部进行拆分，并更改其周围的代码.

You could also consider doing the split outside parse_contents and change the code around it.

我还将尝试记录内容错误的文件名，例如[n for (c, n) in pairs if not c or len(c.split(',')) != 2]).

I would also try to log the filenames for which contents wrong, e.g. [n for (c, n) in pairs if not c or len(c.split(',')) != 2]).

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