Strange priorities in EditorFactory.string_value

[aaronayres35]

Motivated by this comment:
https://github.com/enthought/traitsui/pull/1684/files#r655198812

See relevant code block here:

traitsui/traitsui/editor_factory.py

Lines 190 to 208 in 190b683

	def string_value(self, value, format_func=None):
	""" Returns the text representation of a specified object trait value.
	If the **format_func** attribute is set on the editor factory, then
	this method calls that function to do the formatting. If the
	**format_str** attribute is set on the editor factory, then this
	method uses that string for formatting. If neither attribute is
	set, then this method just calls the appropriate text type to format.
	"""
	if self.format_func is not None:
	return self.format_func(value)
	if self.format_str != "":
	return self.format_str % value
	if format_func is not None:
	return format_func(value)
	return str(value)

The docstring does not mention the format_func kwarg, and it seems strange that one can pass a format_func kwarg explicitly and have it go unused if the factory has its format_func or format_str traits set.

[corranwebster]

I remember going down this rabbit-hole about a year ago. This method is almost always called from Editor.string_value which has the same signature (which is documented), and looking at usage it is the editor's default formatter which gets passed in (but which the EditorFactory has no access to). See

traitsui/traitsui/qt4/enum_editor.py

Line 401 in 6913fa4

label = self.string_value(name, str.capitalize)

for example.

So the intended priority is:

• the format_func declared on the EditorFactory by a user of TraitsUI
• the format_str declared on the EditorFactory by a user of TraitsUI
• an optional formatter passed in by the Editor which is a better default than str for that editor. (Edit: note that an editor may use different - or no - default formatter in different contexts).
• str as a final choice if nothing else is available

The logic could almost certainly be improved, but we'd want to preserve the behaviour.