template.loop_context

Loop iteration metadata accessible asloop inside {% for %}blocks.

Provides index tracking, boundary detection, and utility methods for common iteration patterns. All properties are computed on-access.

Properties: index: 1-based iteration count (1, 2, 3, ...) index0: 0-based iteration count (0, 1, 2, ...) first: True on the first iteration last: True on the final iteration length: Total number of items in the sequence revindex: Reverse 1-based index (counts down to 1) revindex0: Reverse 0-based index (counts down to 0) previtem: Previous item in sequence (None on first) nextitem: Next item in sequence (None on last)

Methods: cycle(*values): Return values[index % len(values)]

Output:

        <ul>
            <li class="odd">1/3: Apple ← First</li>
            <li class="even">2/3: Banana</li>
            <li class="odd">3/3: Cherry ← Last</li>
        </ul>
        ```

Loop iteration metadata for{% async for %}blocks.

Provides index-forward variables only. Size-dependent variables (last, length, revindex, revindex0, nextitem) raiseTemplateRuntimeErrorbecause async iterables cannot be pre-materialized without defeating the purpose of lazy streaming.

The async for-loop drives iteration externally — this class does not implement__aiter__. Instead, advance(item)is called at the top of each loop iteration by the compiled code.

Properties:

index: 1-based iteration count (1, 2, 3, ...)
index0: 0-based iteration count (0, 1, 2, ...)
first: True on the first iteration
previtem: Previous item in sequence (None on first)

Methods:

cycle(*values): Return values[index % len(values)]
advance(item): Update state for current iteration (called by compiled code)

Part of RFC: rfc-async-rendering.