score:4

You don't need (or want) to write anything to a file here. You can create the JSON and return it from a flask method:

from flask import Flask, Response

@app.route('/getMyJson')
def getMyJson():
    json = dataFrame.to_json(orient='records', date_format='iso')
    response = Response(response=json, status=200, mimetype="application/json")
    return(response)

The d3 then becomes:

d3.json("/getMyJson", function (error, data) {
  // ...
  // Operations with those data
  // ...
}

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