class_docstr: Raised when a free `Quantity` is trying to get unlocked.
  
  Parameters
  ----------
  quantity : `Quantity`
      A unlocked quantity.
  *args : positional arguments
      More positional arguments for the exception.
code: def __init__(self, quantity: "Quantity", *args) -> None:
      super().__init__(
          "Cannot unlock quantity that has previously been unlocked: {}.".format(
              quantity
          ),
          *args,
      )
  
imports: from typing import Union
  from numbers import Number
label_desc: Use image node_id 1 to create a new DoubleUnlockedQuantity object from inherited base classes: Exception with example: obj = DoubleUnlockedQuantity(quantity)