def _IsBuildRunning(build_data):
  """Checks whether the build is in progress on buildbot.

  Presence of currentStep element in build JSON indicates build is in progress.

  Args:
    build_data: A dictionary with build data, loaded from buildbot JSON API.

  Returns:
    True if build is in progress, otherwise False.
  """
  current_step = build_data.get('currentStep')
  if (current_step and current_step.get('isStarted') and
      current_step.get('results') is None):
    return True
  return False