Saving temporary file for plotting audio waveform

Question

I am developing a web application in Flask - Python.

My goal is to let the user upload an mp3/wav file. This file will (for the scope of this question) get processed by the server and a picture showing the waveform of the audio file will be shown to the user.

My concern is that I am not experienced with neither Flask nor web applications. I would like this audio file to be saved somewhere temporarily, then get deleted. Similarly, I would like the picture of the waveform to just be shown without being saved after the user sees it. This is because I expect all the mp3/wav files to be different - there is no point in saving them.

Right now I have this method that gets called when a user uploads file:

def handle_file(file):
 filename = secure_filename(file.filename)
 filepath = os.path.join(app.config['UPLOAD_FOLDER'], filename)
 file.save(filepath)
 mir.save_plot(filepath)
 os.remove(filepath)
 plot_filepath = PLOT_FOLDER + 'audio.png'
 return plot_filepath

As you can see, I first save the audio file to a directory in the server, then process it (mir.save_plot does that), then I remove it, and then I return the plot_filepath which will be used in the template to show the final plot picture.

The mir.py file is the following:

import librosa
import plot as plt
def save_plot(filename):
 y, sr = librosa.load(filename)
 plt.plot(y, 'audio', 'time', 'amplitude')

The plot.py file:

import matplotlib.pylab as plt
def plot(vector, name, xlabel=None, ylabel=None):
 plt.figure()
 plt.plot(vector)
 plt.xlabel(xlabel)
 plt.ylabel(ylabel)
 plt.plot()
 plt.savefig('static/plots/' + name)

I feel like my design is poor and there is a better way to do this. Am I right?

The rest of the code:

def allowed_file(filename):
 return '.' in filename and \
 filename.rsplit('.', 1)[1].lower() in ALLOWED_EXTENSIONS
@app.route('/', methods=['GET', 'POST'])
def index():
 if request.method == "GET":
 return render_template('index.html', request="GET")
 else:
 if 'file' not in request.files:
 flash('No file part')
 return redirect(request.url)
 file = request.files['file']
 if file.filename == '':
 flash('No selected file')
 return redirect(request.url)
 if file and allowed_file(file.filename):
 plot_filepath = handle_file(file)
 return render_template('index.html', request="POST", filepath=plot_filepath)

The allowed_file() and majority of index() code are from the Flask docs.

• Mast: "At some point (not visible here)" Why not? We don't mind long posts and actually prefer to see code in it's proper context.
• pavlos163: It used to be in the index @app.route method (delete the file audio.png if it is there before doing anything else) but I actually removed that now, seemed like a bad thing to do.
• pavlos163: What also troubles me is that right now, if more than two users visit the web app and do this simultaneously, there could be an issue. Should I generate unique names for each plot and file? Seems a bit overkill. Is there an automatic way to create temp files in Flask that could do this for me?
• holroy: There isn't really that much to review here, and the code as it stands doesn't really run as we're missing secure_filename, mir?...
• pavlos163: Sure! I just posted the code in mir.py and plot.py.secure_filename is imported from werkzeug.utils. The Flask docs recommended it when uploading files.

Answer 1

Instead of saving file you can create io.BytesIO object and use it instead of file.

Also

 def allowed_file(filename):
 return (
 '.' in filename
 and os.splitext(filename)[1].lower() in ALLOWED_EXTENSIONS
 )

Also maybe you should check content-type header and not only extension.