adding/changing 'text' to an item in a group - enthought

Question

I'm designing a UI with Enthought's TraitsUI, and I can't figure out how to get done what I want...
Here's what I want:
I have Items() in the view that I want to display as either English or SI units. I can change the value in the 'edit' box based on a SI/English button, but I can't figure out how to change the text of the label. For example, if I have an item 'Length, ft [ 3.28]' and convert it to SI, I'd like it to show 'Length, m [ 1.00]'. I can handle the 3.28->1.00 conversion, but can't figure out how to change the 'ft' to 'm'.
Any suggestions?
One thing I've tried is to define a string which holds the units name (like 'm' or 'ft')...then, in the item, I set the label like this:
label = 'Top, '+lengthUnits
This works fine when the view is first built, but it doesn't update the label when I change the units control. Is there some way to force the view to update with all the new values?
Here's a small py program that shows what I'm trying to do (feel free to critique my style :)). I'll also try and add in a couple of images that shows what happens:
# NOTE: This version of the code has been modified so that it works as I want it to :)
# Example trying to change text on a View...
from traits.api \
import HasTraits, Enum, CFloat, String
from traitsui.api \
import View, Group, HGroup, Item, spring
class TestDialog ( HasTraits ):
length = CFloat(1.0)
choose_units = Enum('English', 'SI')
current_units = 'English'
unit_name = String('ft')
ft_to_m = CFloat(3.28)
view = View(
Group(
HGroup(
spring,
Item(name = "length", label = 'Test length'),
Item(name = 'unit_name', style = 'readonly', show_label = False),
spring
),
HGroup(
spring,
Item(name = "choose_units"),
spring
)
),
title = 'Test Changing View Test'
)
def _choose_units_changed(self):
if self.current_units != self.choose_units:
if self.choose_units == 'SI':
self.length /= self.ft_to_m
self.unit_name = 'm'
else:
self.length *= self.ft_to_m
self.unit_name = 'ft'
self.current_units = self.choose_units
# Run the program (if invoked from the command line):
if __name__ == '__main__':
# Create the dialog:
TestIt = TestDialog()
# put the actual dialog up...
TestIt.configure_traits()

Answer 1

Use a notification as described here: http://code.enthought.com/projects/traits/docs/html/traits_user_manual/notification.html
Update in response to updated question:
Right, labels are not dynamically updated. Instead, make a text field that looks like a label, e.g. with:
label_text = String('Test length, English:')
Then display it in your View with something like:
Item("label_text", style='readonly', show_label=False),
You'll probably also want to use an HGroup nested inside your (V)Group, to position it to the left of your "length" display.
Then modify label_text inside your listener.