code: def symmetrize_force_constants(force_constants, level=1):
      
  
      try:
          import phonopy._phonopy as phonoc
          phonoc.perm_trans_symmetrize_fc(force_constants, level)
      except ImportError:
          for i in range(level):
              set_translational_invariance(force_constants)
              set_permutation_symmetry(force_constants)
          set_translational_invariance(force_constants)
docs: Symmetry force constants by translational and permutation symmetries
  
      Note
      ----
      Schemes of symmetrization are slightly different between C and
      python implementations. If these give very different results, the
      original force constants are not reliable anyway.
  
      Parameters
      ----------
      force_constants: ndarray
          Force constants. Symmetrized force constants are overwritten.
          dtype=double
          shape=(n_satom,n_satom,3,3)
      primitive: Primitive
          Primitive cell
      level: int
          Controls the number of times the following steps repeated:
          1) Subtract drift force constants along row and column
          2) Average fc and fc.T