Conditionals

{% if condition %}
  ...
{% elif other %}
  ...
{% else %}
  ...
{% endif %}

Render based on condition truthiness.

Truthiness rules (per Python):

• False, None, 0, "", [], {}: falsy.
• Everything else: truthy.

Expression evaluation:

• Operators: ==, !=, <, >, <=, >=, and, or, not, in.
• {{ x in items }} → check membership.
• {{ name == "Alice" }} → compare.

Operator precedence:

• or lowest.
• and next.
• not higher.
• Comparisons ==, <.
• Arithmetic +, *.

Implementation:

Short-circuit: and returns first falsy or last; or returns first truthy or last. Critical for null guards: {{ user and user.name }}.

Tests (Jinja2):

• {% if x is none %}
• {% if items is iterable %}
• {% if n is divisibleby 3 %}

Custom tests register similar to filters.

Avoid complex logic in templates. If you need three nested ifs, refactor data preparation.