Cog seem to be the type that just evals normal python.code. While many other template-engines replicate code-structures. For example, in Jinja2 you would write something like "{% for i in data %}{{i}}{% endfor %}", which looks kinda like python, and utilizes python-object, but is not real python-code.
Good code at the expense of "syntactic noise" in templates: a suitable tradeoff for the typical use case of short and precise templates with advanced logic backing them (e.g. the DCT coefficient tables linked in another comment) rather than large outputs with simple logic to keep the templates readable (e.g. a dynamic web page, the typical use of Jinja).
