How to flashing a message with link using Flask flash?

Question

I'm creating a web app using Flask to deal with GoogleOpenID, these codes are almost finished, except the flashing message contains a link:

@oid.after_login
def create_or_login(resp):
    user = db_session.query(User).filter_by(email=resp.email).first()
    if user is not None:
        flash('Successfully signed in', 'success')
    else:
        user = User(nickname=resp.fullname, source=GOOGLE, email=resp.email)
        db_session.add(user)
        db_session.commit()
        flash(flashing_message, 'success')
    g.user = user
    session['nickname'] = user.nickname
    return redirect(oid.get_next_url())

It works well when flashing_message is like this: 'Successfully registered, please click here'

But when flashing_message is 'Successfully registered, please click <a href="/me" class="alert-link">here</a>', it doesn't work (flashes nothing) without throwing any Error. Strangely, sentences between flash() and return doesn't work either (did not set session['nickname] or g.user).

Answer 1

The other answers here focus on changing your template to allow all flash messages to be marked as safe, which may not be what you want.

If you just want to mark certain flashed messages as safe, wrap the text passed to flash() in Markup(). (Flask API Docs for Markup)

For example, instead of:

flash('Successfully registered, please click <a href="/me" class="alert-link">here</a>')

Wrap the string in Markup() like this:

flash(Markup('Successfully registered, please click <a href="/me" class="alert-link">here</a>'))

As always, you will need to import Markup from the flask package something like:

from flask import Markup