old_contents: from bidict import bidict
  
  ELE_TO_NUM = bidict({
      'H': 1,
      'C': 6,
      'N': 7,
      'O': 8,
      'F': 9,
      'P': 15,
      'S': 16,
      'Cl': 17,
  })
  TYPE_ORDER = ['1', 'Ar', '2', '3']
  BOND_LENGTHS = {
      "C": {
          "3":   0.62,
          "2":   0.69,
          "Ar": 0.72,
          "1":   0.85,
      },
      "Cl": {
          "1":   1.045,
      },
      "F": {
          "1":   1.23,
      },
      "H": {
          "1":   0.6,
      },
      "N": {
          "3":   0.565,
          "2":   0.63,
          "Ar": 0.655,
          "1":   0.74,
      },
      "O": {
          "3":   0.53,
          "2":   0.59,
          "Ar": 0.62,
          "1":   0.695,
      },
      "P": {
          "2":   0.945,
          "Ar": 0.985,
          "1":   1.11,
      },
      "S": {
          "2":   0.905,
          "Ar": 0.945,
          "1":   1.07,
      },
  }
  # From wiki
  ELECTRONEGATIVITY = {
      "C": 2.55,
      "Cl": 3.16,
      "F": 3.98,
      "H": 2.20,
      "N": 3.04,
      "O": 3.44,
      "P": 2.19,
      "S": 2.58,
  }
  UNKNOWN = 'UNKNOWN'
  
new_contents: from bidict import bidict
  
  ELE_TO_NUM = bidict({
      'H': 1,
      'C': 6,
      'N': 7,
      'O': 8,
      'F': 9,
      'P': 15,
      'S': 16,
      'Cl': 17,
      'Br': 35,
      'I': 53,
      'Se': 34
  })
  TYPE_ORDER = ['1', 'Ar', '2', '3']
  BOND_LENGTHS = {
      "C": {
          "3":   0.62,
          "2":   0.69,
          "Ar": 0.72,
          "1":   0.85,
      },
      "Cl": {
          "1":   1.045,
      },
      "F": {
          "1":   1.23,
      },
      "H": {
          "1":   0.6,
      },
      "N": {
          "3":   0.565,
          "2":   0.63,
          "Ar": 0.655,
          "1":   0.74,
      },
      "O": {
          "3":   0.53,
          "2":   0.59,
          "Ar": 0.62,
          "1":   0.695,
      },
      "P": {
          "2":   0.945,
          "Ar": 0.985,
          "1":   1.11,
      },
      "S": {
          "2":   0.905,
          "Ar": 0.945,
          "1":   1.07,
      },
  }
  # From wiki
  ELECTRONEGATIVITY = {
      "C": 2.55,
      "Cl": 3.16,
      "F": 3.98,
      "H": 2.20,
      "N": 3.04,
      "O": 3.44,
      "P": 2.19,
      "S": 2.58,
  }
  UNKNOWN = 'UNKNOWN'
  
subject: Update constants.py