How do I make a new session in Flask (session.new)

I saw the description of session.new in the Documents

It said: session.new is True if the session is new, False otherwise.

So I tried two things in the following code:

1. session.clear() before requset
2. set permanent_session_lifetime to 1 microsecond

code:

from flask import Flask, render_template, session
from datetime import datetime, timedelta

app = Flask(__name__)
app.config['SECRET_KEY'] = 'hard to guess string'
app.config['permanent_session_lifetime']=timedelta(microseconds=1)

@app.before_request
def clear_session():
    session.permanent=True
    session.clear()

@app.route('/session', methods=['GET','POST'])
def get_session():
    print(session)
    print(session.new)
    return render_template('session.html')

the results are:

<SecureCookieSession {}>
False

Now I have a few questions:

• How do I make session.new to be True?
• If I start a new session, will session.new be True?
• It seems session.clear() can only clear the content of session, am I right?
• How do I start a new session in Flask?