Class enthought.​traits.​trait_types.​ReadOnly

Defines a trait that is write-once, and then read-only. The initial value of the attribute is the special, singleton object Undefined. The trait allows any value to be assigned to the attribute if the current value is the Undefined object. Once any other value is assigned, no further assignment is allowed. Normally, the initial assignment to the attribute is performed in the class constructor, based on information passed to the constructor. If the read-only value is known in advance of run time, use the Constant() function instead of ReadOnly to define the trait.