SQLAlchemy has no attribute Column - python-3.x

Question

Below this is my code i'm learning flask and at this step i'm creating database with flask_sqlachemy. i created an instance of SQLAlchemy that is User, actually i coded like the tutor did but in my case i have this problem, i code this in Pycharm. 'Unresolve attribute refrence Column for class SQLAlchemy' but when i run it there is no error. In the video i saw there is no problem about this. Please help me why pycharm did that!
from flask import Flask, render_template, url_for, flash, redirect
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config['SECRET_KEY'] = '2bd147089908273bb6fd4fd4ce75cf7d'
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///site.db'
db = SQLAlchemy(app)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(20), unique=True, nullable=False)

Answer 1

PyCharm just checks if class SQLAlchemy has an attribute "Column" which it does not. You can resolve your PyCham issue by adding # noinspection PyUnresolvedReferences before your class, i.e.:
# noinspection PyUnresolvedReferences
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(20), unique=True, nullable=False)
Also, as soon as you use an application factory pattern PyCharm will find the 'Column' attributes.
But why are the attributes missing? The answer is in the docstring of the SQLAlchemy object.
This class also provides access to all the SQLAlchemy functions and classes
from the :mod:sqlalchemy and :mod:sqlalchemy.orm modules. So you can
declare models like this:
class User(db.Model):
username = db.Column(db.String(80), unique=True)
pw_hash = db.Column(db.String(80))
[...] If you use these
interfaces through :mod:sqlalchemy and :mod:sqlalchemy.orm directly,
the default query class will be that of :mod:sqlalchemy.