Allow user to provide custom function to generate a line in ScrollMenu

[pkazmier]

Allow user to specify a custom to_str function for the ScrollMenu (and other similar widgets) that would be used to determine the line of text to display on the screen. Currently, only strings are allowed to be added to the widget.

Motivation? Imagine we had a list of Pet objects that might be defined as:

class Pet:
  def __init__(self, name, breed, age):
    self.name = name
    self.breed = breed
    self.age = age

  def purchase(self):
    print(f"You purchased a {self}")

  def __str__(self):
    return f"name={self.name} breed={self.breed} age={self.age}"

To display a list of pets and add an event handler for one that is selected in a ScrollMenu, I'd have to do the following:

pets = [Pet("Baloo", "Dog", 4), Pet("Wilbur", "Horse", 7)]
menu = root.add_scroll_menu("Pets", 0, 0)
menu.add_item_list(str(p) for p in pets) # explicitly convert to string

def process_selection():
  selected_pet_text = menu.get()
  for p in pets:
    if str(p) == selected_pet_text:
      p.purchase()

menu.add_key_command(py_cui.keys.KEY_ENTER, process_selection)

With a very small change to the code, users wouldn't have to look up which Pet was selected because the return value from ScrollMenu.get now returns the actual Pet object itself:

pets = [Pet("Baloo", "Dog", 4), Pet("Wilbur", "Horse", 7)]
menu = root.add_scroll_menu("Pets", 0, 0)
menu.add_item_list(pets) # Allow any object to be added

def process_selection():
  selected_pet_object = menu.get() # this returns the object in the list
  selected_pet_object.purchase()   # so we can use it directly

menu.add_key_command(py_cui.keys.KEY_ENTER, process_selection)

Here is a custom MyScrollMenu that I built to add the above, but it the change is so minor and backwards compatible, that I think it should be added to the widget directly. In the custom widget, I've added one new parameter to the constructor: to_str. It has a default value of str. And then in the body of the ScrollMenu.draw method, only one line is changed—the in clause of the for loop:

class MyScrollMenu(py_cui.widgets.ScrollMenu):
    def __init__(self, id, title, grid, row, column, row_span, column_span, padx, pady, to_str=str,
    ):
        super().__init__(id, title, grid, row, column, row_span, column_span, padx, pady)
        self.to_str = to_str

    def draw(self):
        super(py_cui.widgets.ScrollMenu, self).draw()

        self.renderer.set_color_mode(
            self.selected_color if self.selected else self.color
        )
        self.renderer.draw_border(self)

        counter = self.pady + 1
        line_counter = 0
        for line in (self.to_str(i) for i in self.view_items):
            if line_counter < self.top_view:
                line_counter = line_counter + 1
            else:
                if counter >= self.height - self.pady - 1:
                    break
                if line_counter == self.selected_item:
                    self.renderer.draw_text(
                        self, line, self.start_y + counter, selected=True
                    )
                else:
                    self.renderer.draw_text(self, line, self.start_y + counter)
                counter = counter + 1
                line_counter = line_counter + 1

        self.renderer.unset_color_mode(
            self.selected_color if self.selected else self.color
        )
        self.renderer.reset_cursor(self)

Another nice item with this approach is that one can have multiple ScrollMenu widgets all containing the same Pet list, but each could be displayed differently just by passing a custom to_str function:

pets = [Pet("Baloo", "Dog", 4), Pet("Wilbur", "Horse", 7)]

menu1 = root.add_scroll_menu("Pets Detail", 0, 0)
menu1.add_item_list(pets) # Allow any object to be added

menu2 = root.add_scroll_menu("Pet Names", 0, 0, to_str=lambda p: p.name)
menu2.add_item_list(pets) # Allow any object to be added

[jwlodek]

I like this idea. I want to finish some existing changes I am working on first that make pretty major structural changes to the internals of widgets/popups, and merge those in, and then we can take a look at adding this in the next set of changes.

[jwlodek]

I included this in the v0.1.1 release. At the moment it only supports using the __str__ function, though I may considering the ability to specify a different function in the future.