When Jinja reads a context dictionary, can it read values changed in time?

[Markus Kramer]

From the docs: 

   Template variables are defined by the context dictionary passed to the template.

Saltstack uses Jijna and passes a dictionary called 'grains'.

A Jijna program changes that dictionary.

{% set mygrain_point_in_time1 = grains['mygrain'] %}

{# Change the mygrain key in the grain dictionary #}

{% set mygrain_point_in_time2 = grains['mygrain'] %}

Problem: the second variable has the old, unchanged value.

When does Jijna actually read the context dictionary in the two assigment: 

  - Once at rendering time?

  - Twice, at assigment execution?

If Jinja reads the context dictionary at assigment execution time:

  Can the dictionary be passed a reference?

To sum up the questions: 

  When Jinja reads a context dictionary, can it read values changed in time?