def say_hello(self, widget):
    if self.name_input.value:
        name = self.name_input.value
    else:
        name = 'stranger'
    self.main_window.info_dialog('Hi there!', f'Hello, {name}')
def say_hello(self, widget):
    if self.name_input.value:
        name = self.name_input.value
    else:
        name = 'stranger'
    self.main_window.info_dialog('Hi there!', f'Hello, {name}')