If you create new objects inside your __init__ it may be better to pass them as arguments and have a factory method instead. It separates business logic from technical details on how objects are created. In this example __init__ accepts host and port to construct a database connection: class Query: def __init__(self, host, port): self._connection = Connection(host, port) The possible refactoring is: class Query: def __init__(self, connection): self._connection = connection @classmethod def create(cls, host, port): return cls(Connection(host, port)) This approach has at least these advantages: • It makes dependency injection easy. You can do Query(FakeConnection()) in your tests. • The class can have as many factory methods as needed; the connection may be constructed not only by host and port but also by cloning another connection, reading a config file or object, using the default, etc. • Such factory methods can be turned into asynchronous functions; this is completely impossible for __init__.