Consider this simple minimal example:
from traits.api import Instance, Str, HasTraits
class Person(HasTraits):
name = Str("hooked")
class Chair(HasTraits):
sitting = Instance(Person)
t = Chair()
print t.sitting.name
This fails since t.sitting evaluates to None. Enthought's traits module will enforce that the type of t.sitting is a Person but how can I get the default person to instantiate here? I don't want to pass any parameters to the Chair(**kwargs) I'd like this to be done automatically. The expected output to the print statement is hooked.
This is interesting. According to the Instance docstring, calling Instance will return None if klass is a class and arg and kw are not specified. arg and kw have default values of None and so calling Instance(Person) is returning None like you are seeing. I got your code to work by adding "kw = {}" or "args = []" to the Instance call.
from traits.api import Instance, Str, HasTraits
class Person(HasTraits):
name = Str("hooked")
class Chair(HasTraits):
sitting = Instance(Person, kw = {})
t = Chair()
print t.sitting.name
This prints "hooked" as expected.