How do I join three tables with SQLalchemy and keeping all of the columns in one of the tables?

So, I have three tables:

The class defenitions:

engine = create_engine('sqlite://test.db', echo=False)
SQLSession = sessionmaker(bind=engine)
Base = declarative_base()

class Channel(Base):
    __tablename__ = 'channel'

    id = Column(Integer, primary_key = True)
    title = Column(String)
    description = Column(String)
    link = Column(String)
    pubDate = Column(DateTime)

class User(Base):
    __tablename__ = 'user'

    id = Column(Integer, primary_key = True)
    username = Column(String)
    password = Column(String)
    sessionId = Column(String)

class Subscription(Base):
    __tablename__ = 'subscription'

    userId = Column(Integer, ForeignKey('user.id'), primary_key=True)
    channelId = Column(Integer, ForeignKey('channel.id'), primary_key=True)

NOTE: I know user.username should be unique, need to fix that, and I'm not sure why SQLalchemy creates some row names with the double-quotes.

And I'm trying to come up with a way to retrieve all of the channels, as well as an indication on what channels one particular user (identified by user.sessionId together with user.id) has a subscription on.

For example, say we have four channels: channel1, channel2, channel3, channel4; a user: user1; who has a subscription on channel1 and channel4. The query for user1 would return something like:

channel.id | channel.title | subscribed
---------------------------------------
1            channel1        True
2            channel2        False
3            channel3        False
4            channel4        True

This is a best-case result, but since I have absolutely no clue as how to accomplish the subscribed column, I've been instead trying to get the particular users id in the rows where the user has a subscription and where a subscription is missing, just leave it blank.

The database engine that I'm using together with SQLalchemy atm. is sqlite3

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