Python Code Using Constructors in a Class

Why Constructors Matter: __init__ establishes invariants (required fields, connections, config). In data pipelines, misconfigured objects cause late failures (e.g., missing DB connection at runtime).

Key Points: __new__ creates the object; __init__ initializes it. Never use mutable defaults: def __init__(self, config={})—shared across instances. Use None and assign. For inheritance: always call super().__init__().

Production: Use @dataclass for boilerplate reduction; type hints for clarity. In pipeline classes, validate config in __init__ and fail fast.

class DataPipeline:
def __init__(self, source: str, dest: str, config: dict | None = None):
self.source = source
self.dest = dest
self.config = config or {}