Trait Types

Pyface defines a number of custom Trait types that represent quantities and objects that are useful in the context of graphical user interfaces.

Colors

When working with user interfaces, it is common to want to be able to specify the color to use in part of the UI. Each toolkit usually has its own way of representing colors, and so the ability to specify a color in a toolkit-independent way that can be converted to a toolkit-specific representation is important. This is particularly so when you want to allow the user to specify a color.

Pyface provides a Color class and a corresponding PyfaceColor trait-type that allows this sort of representation. Internally, the Color class stores colors as a tuple of red, green, blue and alpha values which range from 0.0 through to 1.0, inclusive. Helper properties allow the user to specify individual channel values, as well as specify colors in alternate color spaces, such as HSV or HLS:

Color(rgba=(0.4, 0.2, 0.6, 0.8))
Color(red=0.4, green=0.2, blue=0.6, alpha=0.8)
Color(hls=(0.2, 0.5, 0.8))

Color instances can also be created via the from_str() method which allow specification of colors via CSS-style color strings, such as:

Color.from_str("aquamarine")
Color.from_str("#662244")

All standard web colors are understood, as well as hexadecimal RGB(A) with 1, 2 or 4 hex digits per channel.

Color instances are mutable, as their intended use is as values stored in PyfaceColor trait classes which can be modified and listened to. The PyfaceColor validator understands string descriptions of colors, and will accept them as values when initializing or modifying the trait:

class Style(HasStrictTraits):

    color = PyfaceColor("#442266FF")

    @observe('color.rgba')
    def color_changed(self, event):
        print('The color has changed to {}'.format(self.color))

shape = Style(color='orange')
shape.color.blue = 0.8
shape.color = "rebeccapurple"

For interactions with the toolkit, the from_toolkit() and to_toolkit() methods allow conversion to and from the appropriate toolkit color objects, such as Qt’s QColor or wx.Colour. These are most likely to be needed by internal Pyface functionality, and should not be needed by developers who are building applications on top of Pyface.

It is intended that this trait will eventually replace the Color trait from TraitsUI.