from flask import Flask, render_template, request, jsonify, redirect, url_for, flash, session
import json, gc
....

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://postgres:root@localhost/josh'
db = SQLAlchemy(app)

class User(db.Model):
    __tablename__ = "users"
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique = True)
    email = db.Column(db.String(120), unique=True)
    password = db.Column(db.String(100))

    def __init__(self, email):
        self.username = username
        self.email = email
        self.password = password

    def __repr__(self):
        return '<Username %r>' % self.username

@app.route('/register/', methods = ['GET', 'POST'])
def register():
    try:
        if request.method == 'POST':
            username = request.form['username']
            email = request.form['email']
            password = sha256_crypt.encrypt((str(request.form['password'])))

            user = db.session.query(User).filter_by(username = username).first()

            if not user:
                result = User(username, email, password)
                db.session.add(result)
                db.session.commit()

                flash('Thanks for registering!')
                gc.collect()
                session['logged_in'] = True
                session['username'] = username

                return redirect(url_for('dashboard'))

            else:
                flash('That username is already taken, please choose another.')

        return render_template('pages/user_sys/register.html')
    except Exception as e:
        return (str(e))
....