code: def find(self, type_=None, f=None):
          
          for constant in self:
              if type_ is not None and not isinstance(constant, type_):
                  continue
  
              if f is not None and not f(constant):
                  continue
  
              yield constant
docs: Iterates over the pool, yielding each matching ``Constant``. Calling
          without any arguments is equivalent to iterating over the pool.
  
          :param type_: Any subclass of :class:`Constant` or ``None``.
          :param f: Any callable which takes one argument (the constant).