huey: Internal maintenance specification

This class is a compound widget that gives the user two different ways to select a color by its name. They may type the name directly into an Entry widget. Most of the vertical space below this Entry contains a ScrolledList that displays a prefabricated list of color names; the user may instead click on any of these.

# - - - - -   c l a s s   N a m e P i c k e r

class NamePicker(Frame):
    """A compound widget for selecting a color by its name.

      Exports:
        NamePicker ( parent, callback=None ):
          [ (parent is a Frame) and
            (callback is a function or None) ->
              parent  :=  parent with a new NamePicker widget
                  added but not gridded, that calls callback
                  whenever a color is selected
              return that NamePicker widget ]

      Contained widgets:
        .__entryLabel: [ a Label widget that labels self.__entry ]
        .__entry:      [ an Entry widget for entering a color name ]
        .__pickLabel:  [ a Label widget that labels self.__pickList ]
        .__pickList:   [ a ScrolledList widget with color names ]

      Grid plan:  Vertical stacking.

Private attributes include .__callback, the callback function, and a StringVar control variable linked to the .__entry widget.

      State/Invariants:
        .__parent:     [ as passed to constructor ]
        .__callback:   [ as passed to constructor ]
        .__entryVar:
          [ a StringVar control variable for self.__entry ]
    """

The width of the Entry field, a manifest constant, is a class variable.

    NAME_WIDTH  =  20