Slightly more amusingly, but non-equivalently:

  import sys
  from functools import reduce
  from operator import add, sub, mul, truediv as div

  def calc(s, ops=[(add, '+'), (sub, '-'), (mul, '*'), (div, '/')]):
    if not ops:
      return float(s)

    (func, token), *remaining_ops = ops
    return reduce(func, (calc(part, remaining_ops) for part in s.split(token)))

  if __name__ == '__main__':
    print(calc(''.join(sys.argv[1:])))

Does support order of operations, in spite of appearance. Extending to support parentheses is left as an exercise for the reader :)