Pycharm is creating problem for Column(flask_sqlalchemy) when I write a code db.Column(db.String(15), nullable=False)

Question

I have installed flask_sqlalchemy but still pycharm creating following problem Pycharm creating a problem

Unresolved attribute reference 'Column' for class 'SQLAlchemy'

from flask import Flask, render_template, flash, redirect, url_for, session

from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)

app.config['SECRET_KEY'] = '91a80165eabf1265daa8e02eac03600c'

app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///account.db'

db = SQLAlchemy(app)

class Citizen(db.Model):

    firstname = db.Column(db.String(15), nullable=False)
    lastname = db.Column(db.String(15), nullable=False)
    email = db.Column(db.String(150), unique=True, nullable=False)
    password = db.Column(db.String(150), nullable=False)

    def __init__(self, firstname, lastname, email, password):
        self.firstname = firstname
        self.lastname = lastname
        self.email = email
        self.password = password