code: def zfind(cls, **kwargs):
          
          assert len(kwargs) == 1
          fldcond = kwargs.keys()[0].split('__')
          fld = fldcond[0]
          f = cls.__dict__[fld]
          val = kwargs.values()[0]
          if isinstance(val, tuple):
              assert len(val) == 2
              val = (f.typecast_for_write(val[0]), f.typecast_for_write(val[1]))
          else:
              val = f.typecast_for_write(val)
          if len(fldcond) == 1:
              return f.zindex.zfind(eq = val)
          else:
              cond = fldcond[1]
              return f.zindex.zfind(**{cond: val})
docs: Calls typecast_for_write, so it can be used with datetime values,
              or other special field types. For other z* methods,
              typecast_for_write must be called explicitly if needed.