Jinja2 template syntax

Jinja has some neat tricks up it's sleeve for various datatypes.

Block Whitespace

By default every {%...%} gets a newline, which makes configfiles rendered by jinja very ugly.
You can avoid this by adding -%} for your closing block.

{% if foo in bar -%}
Key = Value
{% endif -%}

Dictionaries

dictionaries can be accessed using periods instead of []

{% set foo = {'a': {'b': None}} %}
{{ foo.a.b }}

You can verify the existence of a nested dictionary without KeyError using is defined.
(this works for both dot-dict syntax and traditional dict syntax)

{% set foo = {'a': {'b': None}} %}
{% if foo.a.b.c.d is defined %}
# this will not be rendered
{% endfor %}

Apparently you can also use the default filter to assign values where undefined, but it hasn't worked for me.