Math Expression (mtb)

Documentation

• Class name: Math Expression (mtb)
• Category: mtb/math
• Output node: False

This node is designed to evaluate simple math expressions provided as strings, incorporating the ability to replace placeholders within the expression with specified values. It aims to offer a straightforward method for dynamically calculating numerical results based on input expressions.

Input types

Required

• expression
  • The math expression string to be evaluated. This string can include placeholders for dynamic substitution and supports basic math operations.
  • Comfy dtype: STRING
  • Python dtype: str

Output types

• result (float)
  • Comfy dtype: FLOAT
  • The evaluated result of the math expression as a floating-point number.
  • Python dtype: float
• result (int)
  • Comfy dtype: INT
  • The evaluated result of the math expression, explicitly cast to an integer.
  • Python dtype: int

Usage tips

• Infra type: CPU
• Common nodes: unknown

Source code

class MTB_MathExpression:
    """Node to evaluate a simple math expression string"""

    @classmethod
    def INPUT_TYPES(cls):
        return {
            "required": {
                "expression": ("STRING", {"default": "", "multiline": True}),
            }
        }

    FUNCTION = "eval_expression"
    RETURN_TYPES = ("FLOAT", "INT")
    RETURN_NAMES = ("result (float)", "result (int)")
    CATEGORY = "mtb/math"
    DESCRIPTION = (
        "evaluate a simple math expression string (!! Fallsback to eval)"
    )

    def eval_expression(self, expression, **kwargs):
        from ast import literal_eval

        for key, value in kwargs.items():
            print(f"Replacing placeholder <{key}> with value {value}")
            expression = expression.replace(f"<{key}>", str(value))

        result = -1
        try:
            result = literal_eval(expression)
        except SyntaxError as e:
            raise ValueError(
                f"The expression syntax is wrong '{expression}': {e}"
            ) from e

        except ValueError:
            try:
                expression = expression.replace("^", "**")
                result = eval(expression)
            except Exception as e:
                # Handle any other exceptions and provide a meaningful error message
                raise ValueError(
                    f"Error evaluating expression '{expression}': {e}"
                ) from e

        return (result, int(result))