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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def CreateFile(filename):
 """Create a GCS file with GCS client lib. Args: filename: GCS filename. Returns: The corresponding string blobkey for this GCS file. """

  with gcs.open(filename, 'w') as f:
    f.write('abcde\n')

  blobstore_filename = '/gs' + filename
  return blobstore.create_gs_key(blobstore_filename)