get hash instance of blob content

        :param h: callable hash generator
        :type h: builtin_function_or_method
        :rtype: _hashlib.HASH
        :return: hash instance

def get_blob_hash(self, h=hashlib.md5):
        """
        get hash instance of blob content

        :param h: callable hash generator
        :type h: builtin_function_or_method
        :rtype: _hashlib.HASH
        :return: hash instance
        """
        assert callable(h)
        return h(self.get_blob_data())