使用 Python Flask 从字符串变量中读取并上传 .txt 文件？

Question

I'm trying to build a web app using Python and Flask to convert .JSON to .CSV format.

Here's how it should work. The app programmatically downloads a JSON file from an API and I need to convert to .CSV format and when the user visits the link, it should convert the JSON to .CSV and it should be downloaded automatically and save it in the user's local disk.

Initially, my approach was to download the JSON file in the servers local disk and convert it to CSV file by creating a new file and by using send_file, the user can download the CSV file.

But, since I deployed into Heroku and I realized the Heroku filesystem is temporary and I can't store any files. I had to change the file concept and convert it by storing it to a string variable.

This is how my code looks now after deploying to heroku.

from flask import Flask,render_template,send_file
import requests
import os
import csv
import json
#import urllib.request



app = Flask(__name__,template_folder='templates')

@app.route('/')
def index():
    return render_template('index.html')

@app.route('/jsonParser')
def jsonParser():
    download_url = "https://www....." #link to .JSON file.

    r = requests.get(download_url)
    x = json.loads(r.content)
    outputArray =  ["id", "phones", "email", "firstname", "lastname","role","username","isActive","_created_at","_updated_at"]
    output = ','.join(outputArray)

        try:
            idValue = x["id"] or x["_id"]
            idValue = str(idValue)
        except:
            idValue = x["_id"] or "nil"

        output2 =   ",".join([ idValue ,
                        x["phones"] or "nil",
                        x["email"] or "nil",
                        x["firstname"] or "nil",
                        x["lastname"] or "nil",
                        str(x["role"]) or "nil",
                        x["username"] or "nil",
                       str(x["isActive"]) or "nil" ,

                        str(x["_created_at"]) or "",
                        str(x["_updated_at"]) or ""]) 
        output =  output + "<br>" + output2 #'\n'.join([output, output2])


    return output


if __name__ == "__main__":
    app.run(debug=True,threaded=True)

So now, the output variable consists of the converted .CSV. I'm wondering if there's any way that I can convert it to .txt file so that the user can download it by visiting /jsonParser without storing the .txt file on the server-side.

Answer 1

Is that what you wanted to do? Can you try it like that:

from io import StringIO
from flask import Response

@app.route('/jsonParser')
def jsonParser():

    ...

    output = output + "<br>" + output2  # '\n'.join([output, output2])

    string_out = StringIO()
    string_out.write(output)

    returnfile = string_out.getvalue()

    return Response(returnfile, mimetype="text/plain", headers={"Content-disposition": "attachment; filename=output.txt"})