Give subclasses of the Instance traitlet the option of overriding the klass variable to have a default klass....
Give subclasses of the Instance traitlet the option of overriding the klass variable to have a default klass.
This makes it easy to construct traitlets for specific object types and default metadata. For example, we can have a traitlet for numpy arrays that gives default values for `to_json` and `from_json`:
```python
def np_to_list(a):
if a is not None:
return a.tolist()
def np_from_list(a):
if a is not None:
return np.array(a)
class NDArray(Instance):
klass = np.ndarray
metadata = {'to_json': np_to_list,
'from_json': np_from_list}
```
Then the NDArray traitlet will by default have the klass and some custom metadata.
