code: def get_valid_cwd():
      
      try:
          cwd = _current_dir()
      except:
          warn("Your current directory is invalid. If you open a ticket at " +
              "https://github.com/milkbikis/powerline-shell/issues/new " +
              "we would love to help fix the issue.")
          sys.stdout.write("> ")
          sys.exit(1)
  
      parts = cwd.split(os.sep)
      up = cwd
      while parts and not os.path.exists(up):
          parts.pop()
          up = os.sep.join(parts)
      if cwd != up:
          warn("Your current directory is invalid. Lowest valid directory: "
               + up)
      return cwd
docs: Determine and check the current working directory for validity.
  
      Typically, an directory arises when you checkout a different branch on git
      that doesn't have this directory. When an invalid directory is found, a
      warning is printed to the screen, but the directory is still returned
      as-is, since this is what the shell considers to be the cwd.