Simple Expression Strings

ComfyUI's text nodes are great at one thing: merging a handful of inputs in order. The moment you want anything conditional - "if this is set, add that word", "repeat this character N times", "join these with a separator" - you're either juggling conditional nodes or giving up. Simple Eval Strings lets you write a small expression over three string inputs (a, b, c) and get a composed string back.

The default says it all: a + ' ' + b + c turns "Hello", "World", "!" into "Hello World!". That's the boring case. The useful ones are a.replace("bad", "good"), (b + ", " + c).upper(), or a * 3 when you need a repeated fragment. It's the smallest node in the pack and, for prompt builders, quietly one of the most convenient.

How it works

Same simpleeval engine as the numeric evaluators: a restricted Python expression evaluator, so you get string methods - +, * (repeat), .upper(), .lower(), .replace(), .join(), .strip(), indexing like b[0] - without arbitrary code execution. It's safe to run on workflow-controlled text, which is worth saying out loud given how many custom nodes won't guarantee that.

python_expression is where you type the formula, print_to_console echoes to the terminal for debugging, and the three inputs a/b/c are strings. Everything the expression touches is a string, so no type surprises.

One output: STRING, the evaluation result. That's it - no INT/FLOAT/STRING triple here, because there's only one type in the room.

Install

Ships inside ComfyUI Text Processor:

cd ComfyUI/custom_nodes
git clone https://github.com/rookiestar28/ComfyUI_Text_Processor.git
pip install -r requirements.txt

Restart after. Manager users: "ComfyUI Text Processor".

Gotchas

The inputs are strings even when you type numbers, so a * 2 repeats the text, it doesn't multiply a number - a * 2 with a="3" gives "33". If you need numeric behavior, that's the float/int evaluators' job. And since the expression is a Python subset, quoting matters: use single quotes inside the expression (a + ' ' + b) because the widget itself is one big string. Minor, but it's the classic first-run stumble. For building structured prompts from components - especially with .replace() cleaning up a wildcard or LLM output - this is the node that replaces three others.