I’d like to do an ‘expensive’ calculation, and then download the data as a csv file. The csv file is too long to pass the data as an href. How can I do this? Here’s a working example, I’d like some way to get access to the dataframe ‘df’ that is calculated inside update() and download it as a csv.
import dash
import dash_core_components as dcc
import dash_html_components as html
import pandas as pd
import numpy as np
import flask
import io
from dash.dependencies import Input, Output, State
# import plotly.graph_objs as go
external_stylesheets = ['https://codepen.io/chriddyp/pen/bWLwgP.css']
app = dash.Dash(__name__, external_stylesheets=external_stylesheets)
app.layout = html.Div([
html.Button('Calculate',id='calculate'),
html.A('download',href='download_csv'),
dcc.Store(id='data_store',storage_type='memory'),
])
# Calculate the data and store it.
@app.callback(
Output('data_store', 'data'),
[Input('calculate', 'n_clicks')])
def update(n_clicks):
print('Running expensive calculation...')
# This is the data we want to download:
d = {'col1': np.array(range(1000))}
df = pd.DataFrame.from_dict(d)
return df.to_json()
@app.server.route('/download_csv/')
def download_excel():
# --------------------------------------------------------------------
# ** How do I get access to 'df' that is calculated in update()???
# --------------------------------------------------------------------
# Dummy dataframe for downloading.
d = {'col1': [1, 2], 'col2': [3, 4]}
df = pd.DataFrame(data=d)
#Convert DF
str_io = io.StringIO()
df.to_csv(str_io, sep=",")
mem = io.BytesIO()
mem.write(str_io.getvalue().encode('utf-8'))
mem.seek(0)
str_io.close()
return flask.send_file(mem,
mimetype='text/csv',
attachment_filename='downloadFile.csv',
as_attachment=True)
if __name__ == '__main__':
app.run_server(debug=True)
