Flask : handle successive request.method==["POST"] in the same view

Question

I'm using Flask and a few HTML-CSS-JS templates for an application which involves audio recordings.

I send a blob in a dedicated template (here index.html) as following :

<script type="text/javascript">

  // some stuff with a new MediaRecorder() after clicking on a button, and then :

  mediaRecorder.onstop = function(e) {

    var blob = new Blob(chunks, { 'type' : mime }),
    xmlhttp = new XMLHttpRequest(),
    url = document.URL;

     xmlhttp.open("POST", url, true);
     xmlhttp.setRequestHeader("Content-type", mime);
     xmlhttp.send(blob);
     chunks=[];
  }

</script>

Then, the related part in views.py :

from flask import Flask, render_template, url_for, request, Response

@app.route('/index', methods=["GET","POST"])
def index():
   count_records=-1
   if request.method == 'POST':
      count_records+=1
      f_name = "audio/test"+str(count_records)+".webm"
      blob = request.data
      with open(f_name, 'ab') as f:
         f.write(blob)
      f.close()

I wanted to use count_records variable in order to save a different file after each request.method==["POST"]. It worked perfectly for one file, but not more. After that, got this message on Python console after recording new audio :

File 'audio/test0.webm' already exists. Overwrite ? [y/N] Not overwriting - exiting

So in fact the first request.method is always valid, and I didn't figure out how to manage that... Is this posible ?

EDIT

1. I want use one and only one view to achieve this (from /index to /index), not pass a variable from an other similar view (from /a to /b)

2. The user starts/stopped every MediaRecorder, he is involved in the process

3. As you see, the question supposed answer to the question not answers as well...

EDIT 2

A timestamp with datetime.datetime.now() fixed the problem. Not a Flask session as the bad-called answering post...