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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 path(self):
 """Returns the build root for the current workspace."""

    if self._root_dir is None:
      # This env variable is for testing purpose.
      override_buildroot = os.environ.get('PANTS_BUILDROOT_OVERRIDE', None)
      if override_buildroot:
        self._root_dir = override_buildroot
      else:
        self._root_dir = os.path.realpath(self.find_buildroot())
      if PY2:
        self._root_dir = self._root_dir.decode('utf-8')
    return self._root_dir