From flask docs: Flask’s Context Processors
To inject new variables automatically into the context of a template,
context processors exist in Flask. Context processors run before the
template is rendered and have the ability to inject new values into
the template context. A context processor is a function that returns a
dictionary. The keys and values of this dictionary are then merged
with the template context, for all templates in the app:
Example from docs:
@app.context_processor
def inject_user():
return dict(user=g.user)
Note that this example uses the g variable, which is already accessible in templates.