I can't create a database with SQLAlchemy

I'm really having trouble trying to understand SQLAlchemy so I apologize if this is a really symplistic problem. I can't find the sqlite database in any of my directories when I run the following code.

from sqlalchemy import create_engine, Column, Integer, String
from sqlalchemy.ext.declarative import declarative_base


engine = create_engine('sqlite:///:memory:', echo=True)
Base = declarative_base()

class User(Base):
     __tablename__ = 'users'

     id = Column(Integer, primary_key=True)
     name = Column(String)
     fullname = Column(String)
     password = Column(String)

     def __repr__(self):
         return "<User(name='%s', fullname='%s', password='%s')>" % (
                             self.name, self.fullname, self.password)


Base.metadata.create_all(engine)