reverse polish evaluator in python

reverse_polish_evaluator.py

# This example assumes binary operators, but this is easy to extend.
# Comes from this excellent article: http://blog.reverberate.org/2013/07/ll-and-lr-parsing-demystified.html
ops = {
  "+": (lambda a, b: a + b),
  "-": (lambda a, b: a - b),
  "*": (lambda a, b: a * b),
  "/": (lambda a, b: a / b)
}

def eval(expression):
  tokens = expression.split()
  stack = []

  for token in tokens:
    if token in ops:
      arg2 = stack.pop()
      arg1 = stack.pop()
      result = ops[token](arg1, arg2)
      stack.append(result)
    else:
      # if it's not an operator it's a number
      stack.append(float(token))

  return stack.pop()
  
print(eval("1 2 + "))
print(eval("990 1 2 + *"))
print(eval("1000 990 1 2 + * +"))
print(eval("1000 990.4 1 2 + * +"))

float for a more general case