wxPython DND file loader panel

import wx
from pathlib import Path

class DNDButton(wx.Panel):
    """wxPython Drag & Drop file loader panel

    Simple DND button with a title bar.
    Drop files on the button or click the button to load files.
    The button also displays the first loaded file's name with file count.
    """

    def __init__(self, parent, title, listener=lambda files: True, wildcard='All files|*.*'):
        """Default initializer.

        parent: wx.Window
        title: str
        listener: (files: list[str] -> Boolean) (True: Keep files, False: Clear files)
        wildcard: str
        """
        wx.Panel.__init__(self, parent)
        self.SetMinSize((0, 0)) # override minsize for text wrapping

        self.list = []
        self.listener = listener
        self.wildcard = wildcard

        sizer = wx.BoxSizer(wx.VERTICAL)
        self.SetSizer(sizer)

        self.label = wx.StaticText(self, label=title)
        sizer.Add(self.label, flag=wx.CENTER)

        self.button = wx.Button(self, label='Drop files here\nor click to select files')
        sizer.Add(self.button, flag=wx.UP|wx.EXPAND, border=5, proportion=1)
        self.button.Bind(wx.EVT_BUTTON, self.onOpenFiles)
        self.button.SetDropTarget(self.FileDrop(self))

        self.Layout()

    def onOpenFiles(self, evt):
        with wx.FileDialog(self, 'Open files', wildcard=self.wildcard, style=wx.FD_OPEN | wx.FD_FILE_MUST_EXIST | wx.FD_MULTIPLE) as fileDialog:
            if fileDialog.ShowModal() == wx.ID_CANCEL:
                return

            files = fileDialog.GetPaths()
            self.onFilesAdded(files)

    def onFilesAdded(self, files):
        # set list
        self.list = files

        # check if empty
        if len(self.list) == 0:
            self.button.SetLabel('Drop files here\nor click to select files')
            return

        # set button label
        first_filename = Path(self.list[0]).name

        if len(self.list) == 1:
            self.button.SetLabel(f' \n{first_filename}\n ') # inserting linebreaks enables the button to wrap the text
        else:
            self.button.SetLabel(f'{first_filename}\nTotal {len(self.list)} files')

        # check listener
        valid = self.listener(self.list)
        if not valid:
            self.clearFiles()

    def clearFiles(self):
        """Clear all files
        """
        self.onFilesAdded([])

    class FileDrop(wx.FileDropTarget):
        def __init__(self, parent):
            wx.FileDropTarget.__init__(self)
            self.parent = parent

        def OnDropFiles(self, x, y, filenames):
            self.parent.onFilesAdded(filenames)
            return True