class_docstr: Class for running FiftyOne migrations.
  
  Args:
      head: the current revision
      destination: the destination revision
class_docstr_tok: ["Class","for","running","FiftyOne","migrations",".","Args",":","head",":","the","current","revision","destination",":","the","destination","revision"]
docstr: The head revision.
docstr_tok: ["The","head","revision","."]
code: def head(self):
      """The head revision."""
      return self._head
  
imports: import bisect
  import logging
  import os
  from packaging.requirements import Requirement
  from packaging.version import Version
  import eta.core.utils
  import fiftyone
  import fiftyone.constants
  import fiftyone.core.odm
  import fiftyone.core.utils
label_desc: Use image node_id 2 for calling the MigrationRunner obj's underlying member method code with example usage: obj.head() and returns: self