Can you explain what metadata is in the ORM library SQLAlchemy?

In SQLAlchemy, metadata is an object that contains information about the database structure: tables, columns, relationships, and constraints. Metadata describes the database schema as Python objects, allowing the ORM to automatically create and manage tables.

For example, the MetaData object holds a collection of Table objects, each describing a table and its columns:

from sqlalchemy import MetaData, Table, Column, Integer, String

metadata = MetaData()

users = Table('users', metadata,
              Column('id', Integer, primary_key=True),
              Column('name', String),
              Column('age', Integer))

Metadata allows SQLAlchemy to create tables in the database and provides a link between Python objects and tables.