• TraitsUI

TraitsUI is a module that allows automatic generation of WxPython dialogs to edit the properties of objects.

It makes building interactive graphical user interfaces much easier than working directly with the widgets.

This page is nothing but a short introduction. A step-by-step tutorial on building an interactive scientific application with TraitsUI is available at: http://gael-varoquaux.info/computers/traits_tutorial/index.html .

The configure_traits dialog

A "traited" object is an object whose attributes have been specified beforehand.

from enthought.traits.api import Str, Int, HasTraits
class Person(HasTraits):
    age = Int
    name = Str

The "HasTraits" metaclass will check that the values the attributes are set to correspond to the object's definition.

>>> joe = Person()
>>> joe.name = "joe"
>>> joe.age = "1"
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/local/lib/python2.4/site-packages/enthought/traits/trait_handlers.py", line 171, in error
    raise TraitError, ( object, name, self.info(), value )
enthought.traits.trait_errors.TraitError: The 'age' trait of a Person instance must be a value of type 'int', but a value of 1 was specified.

A traited object has a method that can display a dialog to edit its attributes:

>>> joe.configure_traits()

Interactive dialogs

The "configure_traits" method does not fit in a larger UI, it creates a UI, with its event-loop, and closes it once the dialog is closed. It fits in purely sequential batch programming.

Using a few simple modification notifications makes the application interactive:

from enthought.traits.api import Str, Float, HasTraits
class UnitConverter(HasTraits):
    pounds = Float(0, desc="Weight in pounds")
    kilogrammes  = Float(0, desc="Weight in kilogrammes")
    def _pounds_changed(self, value):
        self.kilogrammes = value/2.2
    def _kilogrammes_changed(self, value):
        self.pounds = value*2.2
UnitConverter().configure_traits()

An "edit_traits" method is available to create a dialog that will be part of the WxPython event-loop. You can use it in "ipython -wthread", that has the WxPython loop running, or in a larger WxPython application. The tutorial shows how to integrate traits and matplotlib plots. Here's another recipe for embedding a matplotlib figure in a TraitsUI app.

The examples shown here are very basic, but the traits module provides many more tools and features that help building a fully-fledged application for scientific purposes.