docs: def get_states(self):
          """
          Returns the states of variables present in the network
  
          Example
          -----------
          >>> from pgmpy.readwrite import BIFReader
          >>> reader = BIFReader("bif_test.bif")
          >>> reader.get_states()
          {'bowel-problem': ['true','false'],
          'dog-out': ['true','false'],
          'family-out': ['true','false'],
          'hear-bark': ['true','false'],
          'light-on': ['true','false']}
          """
          variable_states = {}
          for block in self.variable_block():
              name = self.name_expr.searchString(block)[0][0]
              variable_states[name] = list(self.state_expr.searchString(block)[0][0])
  
          return variable_states