parameters: (self, prop, handler)
docstring: Watches for a property to be assigned a value and runs a function when that occurs.
docstring_summary: Watches for a property to be assigned a value and runs a function when that occurs.
docstring_tokens: Watches for a property to be assigned a value and runs a function when that occurs .
function: def watch(self, prop, handler):
          "Watches for a property to be assigned a value and runs a function when that occurs."
          self.__watchpoints__[prop] = handler
function_tokens: def watch ( self , prop , handler ) : self . __watchpoints__ [ prop ] = handler