docs: def __parse_chemical_data():
      '''Gets and parses file'''
      filename = get_file('chemical_data.tsv')
  
      with io.open(filename, 'r', encoding='cp1252') as textfile:
          next(textfile)
  
          for line in textfile:
              tokens = line.strip().split('\t')
  
              if tokens[3] == 'FORMULA':
                  # Many seemingly contradictory formulae exist,
                  # depending upon the source database
                  chebi_id = int(tokens[1])
  
                  if chebi_id not in __FORMULAE:
                      __FORMULAE[chebi_id] = []
  
                  # Append formula:
                  form = Formula(tokens[4], tokens[2])
                  __FORMULAE[chebi_id].append(form)
  
              elif tokens[3] == 'MASS':
                  __MASSES[int(tokens[1])] = float(tokens[4])
  
              elif tokens[3] == 'CHARGE':
                  __CHARGES[int(tokens[1])] = int(tokens[4]
                                                  if tokens[4][-1] != '-'
                                                  else '-' + tokens[4][:-1])