def _merge_method(self, key):
if key in self:<EOL><INDENT>for method in ["<STR_LIT>", "<STR_LIT>"]:<EOL><INDENT>if hasattr(self[key], method):<EOL><INDENT>return method<EOL><DEDENT><DEDENT><DEDENT>return None<EOL>
Identify a merge compatible method available in self[key]. Currently we
support 'update' and 'append'.

:param key: Attribute name or item key
:return: Method name usable to merge a value into the instance mapped
        by key
:rtype: str