old_contents: """Utility for changing directories and execution of commands in a subshell."""
  
  import os, shlex, subprocess
  
  # Store the previous working directory for the 'cd -' command.
  class Holder:
      """Holds the _prev_dir_ class attribute for chdir() function."""
      _prev_dir_ = None
  
      @classmethod
      def prev_dir(cls):
          return cls._prev_dir_
  
      @classmethod
      def swap(cls, dir):
          cls._prev_dir_ = dir
  
  def chdir(debugger, args, result, dict):
      """
      Change the working directory, or cd to ${HOME}.
      You can also issue 'cd -' to change to the previous working directory.    
      """
      new_dir = args.strip()
      if not new_dir:
          new_dir = os.path.expanduser('~')
      elif new_dir == '-':
          if not Holder.prev_dir():
              # Bad directory, not changing.
              print "bad directory, not changing"
              return
          else:
              new_dir = Holder.prev_dir()
  
      Holder.swap(os.getcwd())
      os.chdir(new_dir)
      print "Current working directory: %s" % os.getcwd()
  
  def system(debugger, command_line, result, dict):
      """Execute the command (a string) in a subshell."""
      args = shlex.split(command_line)
      process = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
      output, error = process.communicate()
      retcode = process.poll()
      if output and error:
          print "stdout=>\n", output
          print "stderr=>\n", error
      elif output:
          print output
      elif error:
          print error
      print "retcode:", retcode
  
new_contents: """Utility for changing directories and execution of commands in a subshell."""
  
  import os, shlex, subprocess
  
  # Store the previous working directory for the 'cd -' command.
  class Holder:
      """Holds the _prev_dir_ class attribute for chdir() function."""
      _prev_dir_ = None
  
      @classmethod
      def prev_dir(cls):
          return cls._prev_dir_
  
      @classmethod
      def swap(cls, dir):
          cls._prev_dir_ = dir
  
  def chdir(debugger, args, result, dict):
      """Change the working directory, or cd to ${HOME}.
      You can also issue 'cd -' to change to the previous working directory."""
      new_dir = args.strip()
      if not new_dir:
          new_dir = os.path.expanduser('~')
      elif new_dir == '-':
          if not Holder.prev_dir():
              # Bad directory, not changing.
              print "bad directory, not changing"
              return
          else:
              new_dir = Holder.prev_dir()
  
      Holder.swap(os.getcwd())
      os.chdir(new_dir)
      print "Current working directory: %s" % os.getcwd()
  
  def system(debugger, command_line, result, dict):
      """Execute the command (a string) in a subshell."""
      args = shlex.split(command_line)
      process = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
      output, error = process.communicate()
      retcode = process.poll()
      if output and error:
          print "stdout=>\n", output
          print "stderr=>\n", error
      elif output:
          print output
      elif error:
          print error
      print "retcode:", retcode
  
subject: Remove extra newline in the docstring.