text: import os
  
  os_name = os.name
  path_separator = os.path.sep
  
  
  def is_win():
      global os_name
      return os_name == 'nt'
  
  
  def is_linux():
      global os_name
      return os_name == 'posix'
  
  
  def is_mac():
      global os_name
      return os_name == 'mac'
  
  
  def path_sep():
      global path_separator
      return path_separator
  
  
  def is_pty_supported():
      return is_linux()
  
  
  # THIS SHOULD BE USED IN TESTS ONLY!
  def reset_os():
      global os_name
      global path_separator
  
      os_name = os.name
      path_separator = os.path.sep
  
  
  def set_win():
      global os_name
      global path_separator
      os_name = 'nt'
      path_separator = '\\'
  
  
  def set_linux():
      global os_name
      global path_separator
      os_name = 'posix'
      path_separator = '/'
  
  
  def set_mac():
      global os_name
      global path_separator
      os_name = 'mac'
      path_separator = '/'
  