List Extend

Concatenate two lists without modifying either one. That's the whole node: list_a plus list_b, appended in order, returned as a fresh list. It's the kind of utility that looks trivial until you're building a workflow that needs to merge "base styles" with "extra tags" or combine two batches of prompts before a fan-out, and suddenly you're very happy it exists.

Here's the thing you need to know before you drop it in: this specific class is deprecated. The source marks it DEPRECATED = True with the internal name ListExtendDEPRECATED(batch). It still works - the code path is intact - but sfinktah moved the maintained versions into the *Ovum family (ListExtendOvum for Python lists, plus the Concat/Extend variants in the data utilities). If you're building new graphs, use ListExtendOvum. If you loaded an old workflow that references this class, leave it alone; it'll keep running.

How it works

Two inputs, one output, straight from the schema:

• list_a - the first list.
• list_b - the second list, whose elements get appended after list_a's.

Both are typed * (any), so they work with lists of strings, ints, or even lists of image objects. The output is a new list containing list_a's elements followed by list_b's - importantly, it does not mutate list_a or list_b. That's the "Extend vs append" difference: if you need the original lists to stay intact for other branches of the graph, this is the non-destructive choice (the pack's ListSplice node, by contrast, does mutate in place - different tool for a different job).

A shared quirk of this list family: NewPointer forces IS_CHANGED to return NaN, so the node never caches and always re-executes. Fine for loops, mildly wasteful otherwise.

Where you reach for it

• Merging prompt ingredients. Concatenate a fixed style list with a variable tag list before joining them into a prompt string downstream.
• Combining batch sources. If two branches each produce a list of filenames or seeds, extend merges them into one list for a single fan-out.
• Building a working copy. Since it's non-mutating, you can use it to append to a list you still need elsewhere, without a copy node.

Install

Part of comfy-ovum, so install once:

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

or search comfy-ovum in ComfyUI Manager and restart. No models, no keys.

Gotchas

• It's deprecated - the menu may show it under a "DEPRECATED(batch)"-style name. Grab ListExtendOvum for new work.
• Non-list inputs raise a ValueError (Input must be a Python list), so convert upstream.
• It concatenates, it doesn't dedupe - if both lists contain the same value, you get both copies. For dedup, the pack has UniqueList.