code: def show_qt(qt_class, modal=False, onshow_event=None, force_style=True):
      
      dialog = None
      anchor = sianchor()
      # look for a previous instance
      for d in anchor.children():
          if isinstance(d, qt_class):
              dialog = d
      # if there's no previous instance then create a new one
      if dialog is None:
          dialog = qt_class(anchor)
      # execute callback
      if onshow_event:
          onshow_event(dialog)
      # stylize and gc
      if force_style:
          set_style(dialog, not isinstance(dialog, QtGui.QMenu))
      dialog.setAttribute(QtCore.Qt.WA_DeleteOnClose)
      # show dialog
      if modal:
          dialog.exec_()
      else:
          dialog.show()
          dialog.raise_()  # ensures dialog window is on top
      return dialog
docs: Shows and raise a pyqt window inside softimage ensuring it's not duplicated
      (if it's duplicated then raise the old one).
      qt_class argument should be a class/subclass of QMainWindow, QDialog or any
      top-level window supported by PyQtForSoftimage plugin.
      onshow_event provides a way to pass a function to execute before the window
      is showed on screen, it can be specially handy on modal windows.
      Returns the qt_class instance.