To launch the UI, we will add a simple function to the __init__.py file in the gui module:

import sys
from PyQt4.QtGui import QApplication
from UnitConverter import UnitConverter

The run_gui function is used to create a new Qt application and start a new instance of the unit converter user interface. This is the function that will be called by the launch command that we set in the package in the next section.

def run_gui():
    app = QApplication(sys.argv)
    ui_window = UnitConverter(None)
    ui_window.show()
    app.exec_()