def _where(self, **kwargs):
        '''use this to filter VLists with kv pairs'''
        out = self
        for k,v in kwargs.items():
            out = out.where(k, lambda i:i==v)
        return out
def _where ( self , ** kwargs ) : out = self for k , v in kwargs . items ( ) : out = out . where ( k , lambda i : i == v ) return out
use this to filter VLists with kv pairs