Plot a PNG using matplotlib in a web request, using Flask.

app.py

"Plot a PNG using matplotlib in a web request, using Flask."

# Install dependencies, preferably in a virtualenv:
#
#     pip install flask matplotlib
#
# Run the development server:
#
#     python app.py
#
# Go to http://localhost:5000/plot.png and see a plot of random data.

import random
import StringIO

from flask import Flask, make_response
from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
from matplotlib.figure import Figure


app = Flask(__name__)


@app.route('/plot.png')
def plot():
    fig = Figure()
    axis = fig.add_subplot(1, 1, 1)

    xs = range(100)
    ys = [random.randint(1, 50) for x in xs]

    axis.plot(xs, ys)
    canvas = FigureCanvas(fig)
    output = StringIO.StringIO()
    canvas.print_png(output)
    response = make_response(output.getvalue())
    response.mimetype = 'image/png'
    return response


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

is there a way to embed this response into html template? I have been searching everywhere but have not been able to find a workaround

You saved my life :). Very helpful!

ran the code with slight modification

from flask import send_file
@route("/reports/")
def reports():
    return render_template('report.html')

@app.route('/fig/')
def fig():
  fig = plt.figure()
......
.....
.....
  img = io.BytesIO()
  fig.savefig(img)
  img.seek(0)
  return send_file(img, mimetype='image/png')

report HTML:
<img src="{{ url_for('fig') }}" alt="Image Placeholder">

I am using python3.5 and ran the code with slight modification:

1. Instead of import StringIO, I used import io
2. Instead of output = StringIO.StringIO(), I used output = io.BytesIO()

Thanks

Very helpful, thanks!