Math Expression Solver

Want to compute a * (b + 10)? ComfyUI's "proper" way is a chain of at least two math nodes plus an addition - and God help you when the formula has three levels of parentheses. Math Expression Solver is the shortcut: you type the whole formula into one string field, feed in two values, and get the answer. It's the pack's answer to the question "why is arithmetic in a node graph so much work?"

It's part of DebugPadawan's ComfyUI Essentials, a small MIT-licensed utility pack. Think of it as the budget version of rgthree's Power Puter - less capable, but also a whole lot simpler.

How it works

The expression string is evaluated with Python's eval(), but behind a deliberately locked-down namespace: only a, b, math, abs, round, min, and max are available, and __builtins__ is disabled. The author's own comment in the source is honest about this - "BE CAREFUL: Uses eval()" - and recommends keeping it strictly math-only. Within that sandbox you can write things like:

• a * (b + 10)
• max(a, b) * 2
• round(a / b, 2)
• math.sqrt(a ** 2 + b ** 2)

On any error, the node doesn't crash - it prints [MathExpression Error] ... to the console and returns 0.0 / 0.

The gotchas that will bite you

• Only a and b are in scope. This is the big one. You cannot reference other node outputs by name inside the expression - every value you want in the formula has to be wired into a or b first. Two inputs means two variables; anything more and you're chaining this node.
• Failures are silent in the graph. A typo in the expression gives you 0.0 and a console line you might never see. If the output is always zero, suspect the expression before the math.
• int_val truncates. float_val is the true result; int_val is int() of it. Use the float output if precision matters.

Inputs and outputs

• expression - the formula, a STRING (default a * (b + 10)).
• a, b - the two FLOAT variables, default 1.

Outputs: float_val (FLOAT) and int_val (INT).

Install

Standard custom-node fare:

cd ComfyUI/custom_nodes
git clone https://github.com/DebugPadawan/DebugPadawans-ComfyUI-Essentials.git

Restart ComfyUI, or install via ComfyUI Manager by searching "DebugPadawan". requirements.txt lists numpy, torch, and opencv-python - numpy and torch already ship with ComfyUI and the shipped code never imports cv2, so no heavy downloads, no model files, no API keys.

When to reach for it

Anytime a formula would take three or more math nodes to express - a weighted blend, a scaled offset, a conditional-pick via max. Just remember the sandbox: two variables in, formula in the box, result out. For anything more ambitious, rgthree's Power Puter or an Evaluate/Execute node is the bigger hammer.