generate_figure.py

from flask import render_template
import io
import base64

from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
from matplotlib.figure import Figure

@app.route("/mysuperplot", methods=["GET"])
def plotView():

    # Generate plot
    fig = Figure()
    axis = fig.add_subplot(1, 1, 1)
    axis.set_title("title")
    axis.set_xlabel("x-axis")
    axis.set_ylabel("y-axis")
    axis.grid()
    axis.plot(range(5), range(5), "ro-")

    # Convert plot to PNG image
    pngImage = io.BytesIO()
    FigureCanvas(fig).print_png(pngImage)

    # Encode PNG image to base64 string
    pngImageB64String = "data:image/png;base64,"
    pngImageB64String += base64.b64encode(pngImage.getvalue()).decode('utf8')

    return render_template("image.html", image=pngImageB64String)

# In the image.html jinja2 template use the following <img> to add the plot:
# <img src="{{ image }}"/>