How To delete a saved file after sending the file as an attachment in flask

What the code down below does is accept a file and perform some operation. After that it generates some other file and send it as an attachment. After the file has been sent How could i delete that file.

from flask import Flask, render_template, request, redirect, url_for, send_file, session, flash
from additional import * 
import os
import time
import json

app = Flask(__name__)
app.secret_key = " not 'soo secret' key"

@app.route('/', methods=['GET', 'POST'])
def index():
    if request.method == 'POST':
        form = request.form
        file = request.files['file_name']
        try:
            splited_name = allowed_file(file.filename)
            if splited_name[-1] == "txt":
                file_contents = file.readlines()
                file_contents = to_utf8(file_contents)

                session['file_name'] = splited_name[0] + "." + str(time.time()) + '.txt'
                
                if request.form['crypt'] == "encrypt": 
                    with open("downloads/" + session['file_name'], "w") as f:
                        f.writelines(decrypted_text(file_contents))
                
                if request.form['crypt'] == "decrypt":
                    with open("downloads/" + session['file_name'], "w") as f:
                        f.writelines(encrypted_text(file_contents))               
                
                return redirect(url_for('download_file'))
            else:
                flash("poindi ra mowa")
                return redirect(url_for('index'))
        except Exception:
            return "exception occured"
    return render_template('index.html')

@app.route('/download/file')
def download_file():
    os.remove("downloads/" + session['file_name'])
    return send_file("downloads/" + session['file_name'], as_attachment=True) 



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