def quantity(*args):
    """Create a quantity. This can be from a scalar or vector.

    Example::

      q1 = quantity(1.0, "km/s")
      q2 = quantity("1km/s")
      q1 = quantity([1.0,2.0], "km/s")

    """
    if len(args) == 1:
        if isinstance(args[0], str):
            # use copy constructor to create quantity from string
            return Quantity(from_string(args[0]))
        elif isinstance(args[0], dict):
            if hasattr(args[0]["value"], "__len__"):
                return QuantVec(from_dict_v(args[0]))
            else:
                return Quantity(from_dict(args[0]))
        elif isinstance(args[0], Quantity) or isinstance(args[0], QuantVec):
            return args[0]
        else:
            raise TypeError("Invalid argument type for")
    else:
        if hasattr(args[0], "__len__"):
            return QuantVec(*args)
        else:
            return Quantity(*args)
Create a quantity. This can be from a scalar or vector.

    Example::

      q1 = quantity(1.0, "km/s")
      q2 = quantity("1km/s")
      q1 = quantity([1.0,2.0], "km/s")