Now with arrays

arraytest.py

#!/usr/bin/env python3

class Foo:

	def __init__(self, lhs, op=None, rhs=None):
		self.lhs = lhs
		if op: self.op = op
		if rhs:
			if len(lhs) != len(rhs):
				raise ValueError("Mismatched array sizes")
			self.rhs = rhs

	def __str__(self):
		try:
			return f"({self.lhs} {self.op} {self.rhs})"
		except AttributeError:
			return str(self.lhs)

	def __add__(self, other):
		return Foo(self, "__add__", other)

	def __sub__(self, other):
		return Foo(self, "__sub__", other)

	def __mul__(self, other):
		return Foo(self, "__mul__", other)

	def __truediv__(self, other):
		return Foo(self, "__truediv__", other)

	def __len__(self):
		return len(self.lhs)

	def eval(self, index=None):
		try:
			if index is not None:
				return getattr(self.lhs.eval(index), self.op)(self.rhs.eval(index))
			else:
				return [
					getattr(self.lhs.eval(idx), self.op)(self.rhs.eval(idx))
				for idx in range(len(self))]
		except AttributeError:
			try:
				return self.lhs[index]
			except TypeError:
				return self.lhs


a = Foo([42.0, 34.0])
b = Foo([7.0, 2.0])
c = (a + b) / b
print(c)
print(c.eval())

c = a + (b / b)
print(c)
print(c.eval())

This version works with arrays, and should never hold intermediary values in the expression as arrays in memory

Output:

$ ./arraytest.py
(([42.0, 34.0] __add__ [7.0, 2.0]) __truediv__ [7.0, 2.0])
[7.0, 18.0]
([42.0, 34.0] __add__ ([7.0, 2.0] __truediv__ [7.0, 2.0]))
[43.0, 35.0]