code: def _get_env_var(env_var_name):
      
  
      if env_var_name in os.environ:
          return os.environ[env_var_name]
  
      fname = os.path.join(get_home(), '.tangorc')
      if not os.path.exists(fname):
          if os.name == 'posix':
              fname = "/etc/tangorc"
      if not os.path.exists(fname):
          return None
  
      for line in open(fname):
          strippedline = line.split('#', 1)[0].strip()
  
          if not strippedline:
              # empty line
              continue
  
          tup = strippedline.split('=', 1)
          if len(tup) != 2:
              # illegal line!
              continue
  
          key, val = map(str.strip, tup)
          if key == env_var_name:
              return val
docs: Returns the value for the given environment name
  
      Search order:
  
          * a real environ var
          * HOME/.tangorc
          * /etc/tangorc
  
      :param env_var_name: the environment variable name
      :type env_var_name: str
      :return: the value for the given environment name
      :rtype: str
  
      New in PyTango 7.1.4