Show and Tell - Download Component

Facilitated by the need to enable download of in-memory data, i wrote a Download component some time ago. I have recently updated the code and added a few examples to the documentation. As there has been a number of question of the forum related to downloading data, files, and pandas data frame, i figured it might be of interest to others.

As of version 0.0.15, the basic syntax is like this,

import dash
import dash_html_components as html
from dash.dependencies import Output, Input
from dash_extensions import Download

app = dash.Dash(prevent_initial_callbacks=True)
app.layout = html.Div([html.Button("Download", id="btn"), Download(id="download")])

@app.callback(Output("download", "data"), [Input("btn", "n_clicks")])
def func(n_clicks):
    return dict(content="Hello world!", filename="hello.txt")

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

That is, you just add the component anywhere in the layout (like a Store) and a callback which targets its data property. The data must be in the form of a dictionary with keys content (a string) and filename. To ease the download of files, i have included a file utility function,

import dash
import dash_html_components as html  
from dash.dependencies import Output, Input
from dash_extensions import Download
from dash_extensions.download import send_file

app = dash.Dash(prevent_initial_callbacks=True)
app.layout = html.Div([html.Button("Download", id="btn"), Download(id="download")])

@app.callback(Output("download", "data"), [Input("btn", "n_clicks")])
def func(n_clicks):
    return send_file("/home/emher/Documents/Untitled.png")

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

I just takes the file path and optionally a filename (if you want to rename the file on download). Finally, i have included a utility method for data frames,

import dash
import pandas as pd
import dash_html_components as html

from dash.dependencies import Output, Input
from dash_extensions import Download
from dash_extensions.download import send_data_frame

# Example data.
df = pd.DataFrame({'a': [1, 2, 3, 4], 'b': [2, 1, 5, 6], 'c': ['x', 'x', 'y', 'y']})
# Create app.
app = dash.Dash(prevent_initial_callbacks=True)
app.layout = html.Div([html.Button("Download", id="btn"), Download(id="download")])

@app.callback(Output("download", "data"), [Input("btn", "n_clicks")])
def func(n_nlicks):
    return send_data_frame(df.to_excel, "mydf.xls")
 
if __name__ == '__main__':
    app.run_server()

I haven’t tested it extensively, but it should support all pandas file formats except SQL, i.e. json, html, hdf, feather, parquet, megpack, stata and pickle. I am currently considering moving the component to a separate package, but for the time being, it is part of dash_extensions. If you would like to try it out, it can be installed via pip,

pip install dash-extensions==0.0.15

Happy downloading

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