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Flask: How to use BytesIO in Flask to display matplotlib image without saving in file.

Example shows how to - use BytesIO to create file-like object in memory - save matplotlib image in this object in format png - get data from this object - convert data to string encoded base64 - create HTML image tag with embede image base64

from flask import Flask
#from flask import render_template
import matplotlib.pyplot as plt
import io
import base64

app = Flask(__name__)

@app.route('/plot')
def build_plot():

    img = io.BytesIO()

    y = [1,2,3,4,5]
    x = [0,2,1,3,4]
    plt.plot(x,y)
    plt.savefig(img, format='png')
    img.seek(0)

    plot_url = base64.b64encode(img.getvalue()).decode()

    return '<img src="data:image/png;base64,{}">'.format(plot_url)

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

You can also save matplotlib image as jpg and then you will need jpeg in src="data:image/jpeg;base64,{}".

In similar way you can embed in HTML other files.

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