List Slice Ovum

ListSliceOvum returns a sub-list of your list using JavaScript-style slice semantics, without ever mutating the source. You say "give me the items from index 2 up to index 5," and you get a new list with exactly those elements. It's the maintained Python-list flavor of the pack's slice utility - the deprecated plain ListSlice is the same idea in the old ovum/lists/any family.

Why JS semantics instead of Python's? Because people who build workflows come from everywhere, and slice's rules are forgiving in a way that's genuinely handy in a graph: negative indices count from the end, out-of-range values get clamped instead of erroring, and you can leave the bounds blank. A slice that would be empty in Python's strict world just returns an empty list here.

Inputs and output

• py_list - the source list. Must be a real Python list.
• start - optional, as a STRING widget. Blank → 0. Negative → n + start, clamped to [0, n]. Positive → clamped to [0, n].
• end - optional, also a STRING. Blank → n (the whole rest of the list). Negative → n + end, clamped. The end index is exclusive, so slice(0, 3) grabs items 0, 1, and 2.

Output is a new list containing py_list[start:end]. If start >= end after normalization, you get [] - no error, which is the behavior you want when feeding a possibly-empty result into a loop.

Why "exclusive end" and blank fields matter

Two things trip people up, both by design:

• End is exclusive. start=1, end=3 gives you indices 1 and 2 only. This matches JS and Python, but if you came from a "cut up to and including 3" mental model, you'll wonder why an item vanished.
• Blank ≠ zero for end. Leaving end blank means "to the end of the list." That's how you do "drop the first 2 items": start=2, blank end.

Where you'll use it

• Trimming lists before a fan-out. Take a big list of filenames and slice off the first N before processing.
• Splitting a list into chunks - slice [0:n], [n:2n], etc. to feed parallel branches.
• Loop batches. Inside a repeat loop, use a counter to slice a moving window out of a larger list each iteration.

It's non-mutating, so the original py_list stays intact for other branches - worth remembering when you're juggling several consumers of the same list.

Install

Ships in comfy-ovum:

cd ComfyUI/custom_nodes
git clone https://github.com/sfinktah/comfy-ovum

or ComfyUI Manager → comfy-ovum, then restart. No models, no keys.

Gotchas

• The start/end widgets are strings - a stray space or non-numeric text is treated as "blank," so you may get a bigger slice than you meant. Clean the fields.
• Non-list input raises ValueError: Input must be a Python list.
• start >= end returns an empty list, not an error - make sure downstream nodes can handle empty input, or gate it with isListNotEmpty.