从 Dash/Flask 应用下载动态生成的文件

Question

我试图构建一个 Dash 应用程序的最小示例，它说明了动态生成文件的问题，然后可以通过下载按钮下载该文件。

如果您运行这个例子，您将看到一个可以输入文本的文本区域。单击 "enter" 按钮会将文本存储到一个文件中，并为该文件创建一个下载按钮。

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

import uuid

stylesheets = [
    "https://cdnjs.cloudflare.com/ajax/libs/bulma/0.7.2/css/bulma.min.css", # Bulma
]

# create app
app = dash.Dash(
    __name__,
    external_stylesheets=stylesheets
)


app.layout = html.Div(
    className="section",
    children=[
        dcc.Textarea(
            id="text-area",
            className="textarea",
            placeholder='Enter a value...',
            style={'width': '300px'}
        ),
        html.Button(
            id="enter-button",
            className="button is-large is-outlined",
            children=["enter"]
        ),
        html.Div(
            id="download-area",
            className="block",
            children=[]
        )
    ]
)

def build_download_button(uri):
    """Generates a download button for the resource"""
    button = html.Form(
        action=uri,
        method="get",
        children=[
            html.Button(
                className="button",
                type="submit",
                children=[
                    "download"
                ]
            )
        ]
    )
    return button

@app.callback(
    Output("download-area", "children"),
    [
        Input("enter-button", "n_clicks")
    ],
    [
        State("text-area", "value")
    ]
)
def show_download_button(n_clicks, text):
    # turn text area content into file
    filename = f"{uuid.uuid1()}.txt"
    path = f"downloadable/{filename}"
    with open(path, "w") as file:
        file.write(text)
    uri = path
    return [build_download_button(uri)]


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

但是，生成的 URI 似乎不正确，因为单击按钮只是重定向到索引页面。需要什么才能让它发挥作用？

Answer 1

解决方法在这里：

import uuid

import dash
from dash.dependencies import Input, Output, State
import flask
from flask.helpers import send_file

import dash_core_components as dcc
import dash_html_components as html

stylesheets = [
    "https://cdnjs.cloudflare.com/ajax/libs/bulma/0.7.2/css/bulma.min.css", # Bulma
]

server = flask.Flask('app')

# create app
app = dash.Dash(
    __name__,
    external_stylesheets=stylesheets, 
    server=server                       # <-- do not forget this line
)

# (...) your code here

@server.route("/downloadable/<path>")
def download_file (path = None):
    return send_file("downloadable/" + path, as_attachment=True)

Answer 2

由于 Dash 是基于 Flask 构建的，因此 Flask 无法找到生成的文本文件的 URI。

解决方法是添加flask路由重定向下载资源，官方 plotly dash 存储库中有一个简单的示例， https://github.com/plotly/dash-recipes/blob/master/dash-download-file-link-server.py

下面修改后的代码解决了你的问题

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

import uuid
import os
import flask
stylesheets = [
    "https://cdnjs.cloudflare.com/ajax/libs/bulma/0.7.2/css/bulma.min.css", # Bulma
]

# create app
app = dash.Dash(
    __name__,
    external_stylesheets=stylesheets
)


app.layout = html.Div(
    className="section",
    children=[
        dcc.Textarea(
            id="text-area",
            className="textarea",
            placeholder='Enter a value...',
            style={'width': '300px'}
        ),
        html.Button(
            id="enter-button",
            className="button is-large is-outlined",
            children=["enter"]
        ),
        html.Div(
            id="download-area",
            className="block",
            children=[]
        )
    ]
)

def build_download_button(uri):
    """Generates a download button for the resource"""
    button = html.Form(
        action=uri,
        method="get",
        children=[
            html.Button(
                className="button",
                type="submit",
                children=[
                    "download"
                ]
            )
        ]
    )
    return button

@app.callback(
    Output("download-area", "children"),
    [
        Input("enter-button", "n_clicks")
    ],
    [
        State("text-area", "value")
    ]
)
def show_download_button(n_clicks, text):
    if text == None:
        return
    # turn text area content into file
    filename = f"{uuid.uuid1()}.txt"
    path = f"downloadable/{filename}"
    with open(path, "w") as file:
        file.write(text)
    uri = path
    return [build_download_button(uri)]

@app.server.route('/downloadable/<path:path>')
def serve_static(path):
    root_dir = os.getcwd()
    return flask.send_from_directory(
        os.path.join(root_dir, 'downloadable'), path
    )

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

或者，您可以使用 static 目录而不是 downloadable 目录，它也可以。

有关 flask 静态目录的更多信息： http://flask.pocoo.org/docs/1.0/tutorial/static/

这是片段，

#your code

def show_download_button(n_clicks, text):
    if text == None:
        return
    filename = f"{uuid.uuid1()}.txt"
    path = f"static/{filename}"      # =====> here change the name of the direcotry to point to the static directory
    with open(path, "w") as file:
        file.write(text)
    uri = path
    return [build_download_button(uri)]

#your code

Answer 3

使用 Dash 1.20.0，您现在有一个 dcc.Download 组件用于基于用户的动态下载。它不需要创建自定义按钮，uuid 和 flask.send_file.

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

stylesheets = [
    "https://cdnjs.cloudflare.com/ajax/libs/bulma/0.7.2/css/bulma.min.css", # Bulma
]

# create app
app = dash.Dash(
    __name__,
    external_stylesheets=stylesheets
)


app.layout = html.Div(
    className="section",
    children=[
        dcc.Textarea(
            id="text-area",
            className="textarea",
            placeholder='Enter a value...',
            style={'width': '300px'}
        ),
        html.Button("Enter", id="btn_txt"), 
        dcc.Download(id="download-text")
    ]
)

@app.callback(
    Output("download-text", "data"),
    Input("btn_txt", "n_clicks"),
    State("text-area", "value"),
    prevent_initial_call=True,
)
def create_download_file(n_clicks, text):
    filename = "file.txt"
    # Alternatively:
    # filename = f"{uuid.uuid1()}.txt"

    return dict(content=text, filename=filename)

从 Dash/Flask 应用下载动态生成的文件

Downloading dynamically generated files from a Dash/Flask app

python

flask

plotly-dash