class_docstr: Wraps gfile.ReadableFile to add iteration, enter/exit and readlines.
code: def __next__(self):
      ok, line = self._file.Readline()
      if ok:
          return line
      else:
          raise StopIteration
  
file_path: deepvariant/third_party/nucleus/io/gfile.py
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import six
  from third_party.nucleus.io.python import gfile
label_desc: Use image node_id 5 for calling the ReadableFile obj's underlying member method code with example usage: obj.__next__() and returns: line