Alembic - Add Non-Nullable Column

Add non-nullable column to existing tables in Alembic.

    from alembic import op
    import sqlalchemy as sa
    # ...
    op.add_column('todo', sa.Column('deleted', sa.Boolean(), nullable=True))
    op.execute('UPDATE "todo" SET deleted=false')
    op.alter_column('todo', 'deleted', nullable=False)