code: def fn_check_full(fn):
      
      status = True 
      if not os.path.isfile(fn): 
          status = False
      else:
          try: 
              open(fn) 
          except IOError:
              status = False
      return status
docs: Check for file existence
  
      Avoids race condition, but slower than os.path.exists.
      
      Parameters
      ----------
      fn : str
          Input filename string.
      
      Returns
      -------
      status 
          True if file exists, False otherwise.