Code

app.py or similar

from flask import Flask, render_template, request, redirect, url_for, flash, session, send_from_directory, jsonify, abort
from flask_mysqldb import MySQL, MySQLdb
from werkzeug.utils import secure_filename
from datetime import date
import os
import datetime
import mysql.connector
import MySQLdb.cursors, re
import time

….

UPLOAD_FOLDER = '/pash/to/your/upload/folder'
PIC_UPLOAD_FOLDER = '/pash/to/your/upload/folder'/pictures'
app.config['UPLOAD_FOLDER'] = UPLOAD_FOLDER
app.config['PIC_UPLOAD_FOLDER'] = PIC_UPLOAD_FOLDER
os.makedirs(app.config['UPLOAD_FOLDER'], exist_ok=True)
ALLOWED_EXTENSIONS = {'png', 'jpg', 'jpeg', 'gif', 'pdf'}

app.config['SECRET_KEY'] = 'yoursecretkey'
app.config["MYSQL_USER"] = "db_user_name"
app.config["MYSQL_PASSWORD"] = "db_password"
app.config["MYSQL_DB"] = "db_name"
app.config["MYSQL_CHARSET"] = "utf8mb4"

mysql = MySQL(app)

…
@app.route('/upload', methods=['GET', 'POST'])
def upload_file():
    current_timestamp = str(int(time.time()) // 10000)
    picfolder_path = os.path.join(PIC_UPLOAD_FOLDER, str(current_timestamp))
    picfolder_short = os.path.join('pictures/', str(current_timestamp))
    os.makedirs(picfolder_path, exist_ok=True)
    …..
    if request.method == 'POST':
        if 'file' in request.files:
            pict_file = request.files['file']  ### File from your form
            if pict_file.filename != '':
                 pict_filename = pict_file.filename
                 pict_file.save(os.path.join(app.config['PIC_UPLOAD_FOLDER'], current_timestamp, pict_filename))
   ……
   return redirect(url_for('your form')

return render_template('form/file.html')



P.S. 

Upload folder should hav attribute 775 if you are using external web server (in my case Apache) with other owner (www-data) and Flask and Apache owners in one group.