convert html file to BytesIO then pass as Flask variable

I'm trying to convert a HTML file to BytesIO so that I don't need to write the file in the filesystem and get it from memory instead. I've read this about converting image to BytesIO however I can't apply it to HTML file.

I'm using Flask as my framework.

What i have tried:

buffer = io.BytesIO()

merged_df.to_html(buffer, encoding = 'utf-8', table_uuid = 'seasonality_table')
buffer.seek(0)
html_memory = base64.b64encode(buffer.getvalue())

return render_template('summary_01.html', html_data = html_memory.decode('utf-8'))

then in the HTML code which I want to output the html file:

<img id="picture" src="data:html;base64, {{ html_data }}">

Error message I got = TypeError: expected str, bytes or os.PathLike object, not _io.BytesIO

Solution

First: using <img> to display HTML is totally wrong idea.
Tag <img> is only for images like PNG, JPG, etc.

You can get directly HTML using to_html() without filename

html = merged_df.to_html(table_id='seasonality_table')

and send this as HTML

return render_template('summary_01.html', html_data=html)

and you need safe to display it as HTML

{{ html_data | safe }}

BTW:

If you want to put data as file for downloading then you should use <a> instead of <img> and it may need application/octet-stream instead of html to start downloading it.

html = merged_df.to_html(table_id='seasonality_table')
html = base64.b64encode(html.encode('utf-8')).decode('utf-8')

return render_template('summary_01.html', html_data=html)

<a href="data:application/octet-stream;base64,{{ html_data }}">DOWNLOAD</a>

Minimal working example

from flask import Flask, render_template_string
import pandas as pd
import base64

app = Flask(__name__)

@app.route('/')
def index():

    data = {
        'A': [1,2,3], 
        'B': [4,5,6], 
        'C': [7,8,9]
    }

    df = pd.DataFrame(data)

    html = df.to_html(table_id='seasonality_table')
    
    html_base64 = base64.b64encode(html.encode()).decode()
    
    return render_template_string('''<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
</head>
<body>

{{ html_data | safe }}

<a href="data:application/octet-stream;base64,{{ html_base64 }}">DOWNLOAD</a>

</body>
</html>''', html_data=html, html_base64=html_base64)


if __name__ == '__main__':
    #app.debug = True 
    #app.run(threaded=False, processes=3)
    #app.run(use_reloader=False)
    app.run()