Unresolved attribute reference 'Column' for class 'SQLAlchemy' (Flask)

from flask import Flask, render_template, url_for, flash, redirect
from forms import RegistrationForm, LoginForm
from flask_sqlalchemy import SQLAlchemy
from datetime import datetime

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///site.db'
db = SQLAlchemy(app)

// No idea why this is giving me warnings... it's pretty annoying.

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(20), unique= True, nullable=False) 
    email = db.Column(db.String(80), unique=True, nullable=False)
    image_file = db.Column(db.String(20), unique=True, nullable=False, default='default.jpg')
    password = db.Column(db.String(60), nullable=False)
    posts = db.relationship('Post', backref='author', lazy='true')