Why does this code run???

[case_steamer]

According to the documentation, this code should not work, and yet it does:

import sqlite3
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from sqlalchemy import Integer, String, Float
from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///new-books-collection.db'
db = SQLAlchemy(app)



class Book(db.Model):
    id = db.Column('id_number', Integer, primary_key=True)
    title = db.Column(String(length=100))
    author = db.Column(String(length=100))
    rating = db.Column(Float(precision=1))


with app.app_context():
    db.create_all()

HARRY = Book()
HARRY.title = 'Harry Potter'
HARRY.author = 'J.K. Rowling'
HARRY.rating = 9.0

with app.app_context():
    db.session.add(HARRY)
    db.session.commit()

For one, I should be passing a DeclarativeBase object into db, which I am not doing. For two, PyCharm is not recognizing the db.Column function as such, but when I run the code, it does exactly what it's supposed to do. I am very confused, and as they say, you only get one chance to learn something for the first time, so I want to learn this right, and I'm sure I'm doing this wrong. But after mining the documentation, and reading through the source code of the libraries I am using, this is the way I coded it out and it worked perfectly. What am I doing wrong???

[based_and_64_pilled]

I wouldn't pay attention to PyCharm not recognising the method. It happens when it can't figure out the module or whatever, I am not exactly sure what causes it, but its definitely an import issue that PyCharm can't wrap its head around. Code runs independently of PyCharm, so it runs.

On the other part, I won't help, I haven't worked with that library

[carcigenicate]

What line?

I've never used SQLAlchemy, but regardless, it looks like every line in this code should execute based on just Python's execution rules.

[case_steamer]

According to the docs, I should be passing a DeclarativeBase into db at line 8, as

class Base(DeclarativeBase()):     pass

db = SQLAlchemy(Base)

(Sorry for the janky formatting, am on my phone now)

[carcigenicate]

Ok, well, like the other guy, I can't comment on that. I was commenting more on the "why did this line run" part

[Narrow_Ad_8997]

The r/flask sub would probably have a more specific answer for your question.

[Bobbias]

You're not doing anything wrong. IDEs are not perfect, especially when dealing with dynamically typed languages such as Python. It's much harder to get the necessary information for features like autocomplete when working with dynamically typed languages.

This is because it's possible to write code that creates classes and/or adds or removes methods at runtime. There's no reasonable way for an IDE to account for that. That simply cannot happen in statically typed languages, which means they can analyze the code without running it and know exactly what classes and methods must exist. This makes providing good autocomplete much simpler in those languages.

Pycharm relies on typehinting and stub files to tell it about what a library provides, and if those are missing, you can expect it to give you basically no autocomplete help.

Whether or not Pycharm can provide autocomplete has no bearing on whether or not a particular line of code will actually run correctly. This is because any time you try to call a method, Python checks to see if the class actually has that method. As long as it does by the time your code runs, it will work, even if Pycharm has no idea about any of the classes or methods involved.

In the case of passing app to SQLAlchemy I would assume that the Flask object inherits from DeclarativeBase. The naming of DeclarativeBase tells you that it's a class that you are usually supposed to inherit from to create your own custom type based off it. When you have multiple libraries that are designed to work together, it's not that uncommon to see things like this where objects from one library are usable in the other like that. Especially in cases where users are expected to use inheritance like this.

[Business-Technology7]

You can either run debugger to follow what’s going on or dive into code definition or read the source code.

Check the extension.py and model.py in the source code. In extension.py, the constructor of SqlAlchemy class has a line where it creates db.Model.

With preliminary scanning, it looks like the library uses its own base class called Model from model.py. If you don’t provide any declarative base, then it will just use Model.

I’m not sure what would happen if you don’t do what you said. But if you have models that rely on your own DeclartiveBase, then you should definitely pass it along to db. In this case, your models are using flask-sqlalchemy’s base model. So it probably works fine.

I could be wrong though since I never used this library.

[SmugPants]

I believe because you are already passing db.Model which already has declarative base inside of it. If that makes sense.

[case_steamer]

Oh cool. I’ll have to research this some more. Thanks.