docs: def install():
      """Manual install main script.
      """
      # check installed package
      print("Compare to '%s' ..." % DST)
      need_install_flag = check_need_install()
      if not need_install_flag:
          print("    package is up-to-date, no need to install.")
          return
      print("Difference been found, start installing ...")
  
      # remove __pycache__ folder and *.pyc file
      print("Remove *.pyc file ...")
      pyc_folder_list = list()
      for root, _, basename_list in os.walk(SRC):
          if os.path.basename(root) == "__pycache__":
              pyc_folder_list.append(root)
  
      for folder in pyc_folder_list:
          shutil.rmtree(folder)
      print("    all *.pyc file has been removed.")
  
      # install this package to all python version
      print("Uninstall %s from %s ..." % (PKG_NAME, DST))
      try:
          shutil.rmtree(DST)
          print("    Successfully uninstall %s" % PKG_NAME)
      except Exception as e:
          print("    %s" % e)
  
      print("Install %s to %s ..." % (PKG_NAME, DST))
      shutil.copytree(SRC, DST)
      print("    Complete!")