Get the correct Jinja2 Environment, also for frozen scripts.

def get_env():
    ''' Get the correct Jinja2 Environment, also for frozen scripts.
    '''
    if getattr(sys, 'frozen', False) and hasattr(sys, '_MEIPASS'):
        # PyInstaller uses _MEIPASS and only works with jinja2.FileSystemLoader
        templates_path = join(sys._MEIPASS, 'bokeh', 'core', '_templates')
    else:
        # Non-frozen Python and cx_Freeze can use __file__ directly
        templates_path = join(dirname(__file__), '_templates')

    return Environment(loader=FileSystemLoader(templates_path))