How to make a dataframe download through browser using python

Question

I have a function, which generates a dataframe, which I am exporting as an excel sheet, at the end of the function. df.to_excel('response.xlsx') This excel file is being saved in my working directory. Now I'm hosting this in Streamlit on heroku as a web app, but I want this excel file to be downloaded in user's local disk (a normal browser download) once this function is called. Is there a way to do it ?

Answer 1

Snehan Kekre, from streamlit, wrote the following solution in this thread.

streamlit as st
import pandas as pd
import io

import base64
import os
import json
import pickle
import uuid
import re


def download_button(object_to_download, download_filename, button_text, pickle_it=False):
    """
    Generates a link to download the given object_to_download.
    Params:
    ------
    object_to_download:  The object to be downloaded.
    download_filename (str): filename and extension of file. e.g. mydata.csv,
    some_txt_output.txt download_link_text (str): Text to display for download
    link.
    button_text (str): Text to display on download button (e.g. 'click here to download file')
    pickle_it (bool): If True, pickle file.
    Returns:
    -------
    (str): the anchor tag to download object_to_download
    Examples:
    --------
    download_link(your_df, 'YOUR_DF.csv', 'Click to download data!')
    download_link(your_str, 'YOUR_STRING.txt', 'Click to download text!')
    """
    if pickle_it:
        try:
            object_to_download = pickle.dumps(object_to_download)
        except pickle.PicklingError as e:
            st.write(e)
            return None

    else:
        if isinstance(object_to_download, bytes):
            pass

        elif isinstance(object_to_download, pd.DataFrame):
            #object_to_download = object_to_download.to_csv(index=False)
            towrite = io.BytesIO()
            object_to_download = object_to_download.to_excel(towrite, encoding='utf-8', index=False, header=True)
            towrite.seek(0)

        # Try JSON encode for everything else
        else:
            object_to_download = json.dumps(object_to_download)

    try:
        # some strings <-> bytes conversions necessary here
        b64 = base64.b64encode(object_to_download.encode()).decode()

    except AttributeError as e:
        b64 = base64.b64encode(towrite.read()).decode()

    button_uuid = str(uuid.uuid4()).replace('-', '')
    button_id = re.sub('\d+', '', button_uuid)

    custom_css = f""" 
        <style>
            #{button_id} {{
                display: inline-flex;
                align-items: center;
                justify-content: center;
                background-color: rgb(255, 255, 255);
                color: rgb(38, 39, 48);
                padding: .25rem .75rem;
                position: relative;
                text-decoration: none;
                border-radius: 4px;
                border-width: 1px;
                border-style: solid;
                border-color: rgb(230, 234, 241);
                border-image: initial;
            }} 
            #{button_id}:hover {{
                border-color: rgb(246, 51, 102);
                color: rgb(246, 51, 102);
            }}
            #{button_id}:active {{
                box-shadow: none;
                background-color: rgb(246, 51, 102);
                color: white;
                }}
        </style> """

    dl_link = custom_css + f'<a download="{download_filename}" id="{button_id}" href="data:application/vnd.openxmlformats-officedocument.spreadsheetml.sheet;base64,{b64}">{button_text}</a><br></br>'

    return dl_link


vals= ['A','B','C']
df= pd.DataFrame(vals, columns=["Title"])  

filename = 'my-dataframe.xlsx'
download_button_str = download_button(df, filename, f'Click here to download {filename}', pickle_it=False)
st.markdown(download_button_str, unsafe_allow_html=True)

I'd recommend searching the thread on that discussion forum. There seem to be at least 3-4 alternatives to this code.