Template helpers (that is, everything in ``kallithea.lib.helpers``)

should only be referenced from templates. If you need to call a

helper from the Python code, consider moving the function somewhere

else (e.g. to the model).

Notes on the SQLAlchemy session

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Each HTTP request runs inside an independent SQLAlchemy session (as well

as in an independent database transaction). ``Session`` is the session manager

and factory. ``Session()`` will create a new session on-demand or return the

current session for the active thread. Many database operations are methods on

Database model objects

(almost) always belong to a particular SQLAlchemy session, which means

that SQLAlchemy will ensure that they're kept in sync with the database

(but also means that they cannot be shared across requests).

Objects can be added to the session using ``Session().add``, but this is

rarely needed:

* When creating a database object by calling the constructor directly,

  it must explicitly be added to the session.