code: def Open(filename, mode="r"):
      if mode.startswith("r"):
          return ReadableFile(filename)
      elif mode.startswith("w"):
          return gfile.WritableFile.New(filename)
      else:
          raise ValueError(
              "Unsupported mode '{}' for Open".format(mode)
          )
  
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 3 for calling a global function with example usage: Open(filename, mode) and returns: ReadableFile, gfile