The DelphiVCL and DelphiFMX libraries for Python are a set of Python modules that put the robust and mature VCL and FireMonkey (FMX) GUI libraries in the hands of Python developers.

Check out this sample:

from delphivcl import *

class MainForm(Form):

    def __init__(self, owner):
        self.Caption = "A VCL Form..."
        self.SetBounds(10, 10, 500, 400)
        self.Position = "poScreenCenter"

        self.lblHello = Label(self)
        self.lblHello.SetProps(Parent=self, 
            Caption="Hello DelphiVCL for Python")
        self.lblHello.SetBounds(10, 10, 300, 24)

        self.OnClose = self.__on_form_close


    def __on_form_close(self, sender, action):
        action.Value = caFree


def main():
    Application.Initialize()
    Application.Title = "Hello Python"
    Main = MainForm(Application)
    Main.Show()
    FreeConsole()
    Application.Run()
    Main.Destroy()


main()

Very nice and nostalgic! I used VCL a lot in the 2000s, and was very productive with it. This version is not open source, but has some kind of freeware license. I personally wouldn't use any non-platform-provided UI library that's not open source, for practical reasons.