Your first model in Python

Goal: define a Book model, generate classes.py, and create an instance of the generated class. This tutorial uses no AI calls.

Install BESSER

Use Python 3.11 or 3.12, the versions tested by the project. Create an empty directory for this tutorial and a virtual environment:

python -m venv .venv

Activate it with the command for your shell:

# Windows PowerShell
.\.venv\Scripts\Activate.ps1

# Linux or macOS
source .venv/bin/activate

Then install the library:

python -m pip install besser

To work from an unreleased development build, use the source installation instead.

Define the model and generate code

Save this as first_model.py:

"""The complete example used by the Python getting-started tutorial."""

from besser.BUML.metamodel.structural.structural import (
    Class,
    DomainModel,
    IntegerType,
    Property,
    StringType,
)
from besser.generators.python_classes import PythonGenerator

book = Class(
    name="Book",
    attributes={
        Property(name="title", type=StringType),
        Property(name="pages", type=IntegerType),
    },
)
library = DomainModel(name="Library", types={book}, associations=set())

PythonGenerator(model=library, output_dir="output").generate()

Property defines an attribute, Class collects the attributes, and DomainModel collects the classes. PythonGenerator writes an ordinary Python implementation of the model.

Run the script:

python first_model.py

You should now have output/classes.py containing a Book class with title and pages properties.

Use the generated class

From the same directory, run:

python -c "from output.classes import Book; book = Book(title='Dune', pages=412); print(book.title, book.pages)"

Expected output:

Dune 412

Next steps