how to make a sublime text 3 plugin code example

Example: sublime text write plugin panel

pt = window.get_output_panel("paneltest")
pt.set_read_only(False)
edit = pt.begin_edit()
pt.insert(edit, pt.size(), "Writing...")
pt.end_edit(edit)
window.run_command("show_panel", {"panel": "output.paneltest"})