docs: def _clause_formatter(self, cond):
          '''Formats conditions
          args is a list of ['field', 'operator', 'value']
          '''
  
          if len(cond) == 2 :
              cond = ' '.join(cond)
              return cond
  
          if 'in' in cond[1].lower() :
              if not isinstance(cond[2], (tuple, list)):
                      raise TypeError('("{0}") must be of type <type tuple> or <type list>'.format(cond[2]))
  
              if 'select' not in cond[2][0].lower() :
                  cond[2] = "({0})".format(','.join(map(str,["'{0}'".format(e) for e in cond[2]])))
              else:
                  cond[2] = "({0})".format(','.join(map(str,["{0}".format(e) for e in cond[2]])))
  
              cond = " ".join(cond)
          else: 
              #if isinstance(cond[2], str):
              #    var = re.match('^@(\w+)$', cond[2])
              #else:
              #    var = None
              #if var :
              if isinstance(cond[2], str) and cond[2].startswith('@'):
                  cond[2] = "{0}".format(cond[2])
              else :
                  cond[2] = "'{0}'".format(cond[2])
              cond = ' '.join(cond)
  
          return cond