Won't compile on Python3

[simpleguy677]

Traceback (most recent call last):
File "loki.py", line 10, in
from flask import Flask, render_template, request, session, jsonify, redirect, url_for
ModuleNotFoundError: No module named 'flask'

[simpleguy677]

pip3 install -r requirements.txt

solves the compilation on debian running v2 ans v3 python