<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _merge_legacy(run, full_result, result, index):
 """Merge a result from a legacy opcode into the full results. """

    affected = result.get('n', 0)

    errmsg = result.get("errmsg", result.get("err", ""))
    if errmsg:
        # wtimeout is not considered a hard failure in
        # MongoDB 2.6 so don't treat it like one here.
        if result.get("wtimeout"):
            error_doc = {'errmsg': errmsg, 'code': _WRITE_CONCERN_ERROR}
            full_result['writeConcernErrors'].append(error_doc)
        else:
            code = result.get("code", _UNKNOWN_ERROR)
            error = _make_error(run.index(index), code, errmsg, run.ops[index])
            if "errInfo" in result:
                error["errInfo"] = result["errInfo"]
            full_result["writeErrors"].append(error)
            return
    if run.op_type == _INSERT:
        full_result['nInserted'] += 1
    elif run.op_type == _UPDATE:
        if "upserted" in result:
            doc = {_UINDEX: run.index(index), _UID: result["upserted"]}
            full_result["upserted"].append(doc)
            full_result['nUpserted'] += affected
        # Versions of MongoDB before 2.6 don't return the _id for an
        # upsert if _id is not an ObjectId.
        elif result.get("updatedExisting") is False and affected == 1:
            op = run.ops[index]
            # If _id is in both the update document *and* the query spec
            # the update document _id takes precedence.
            _id = op['u'].get('_id', op['q'].get('_id'))
            doc = {_UINDEX: run.index(index), _UID: _id}
            full_result["upserted"].append(doc)
            full_result['nUpserted'] += affected
        else:
            full_result['nMatched'] += affected

    elif run.op_type == _DELETE:
        full_result['nRemoved'] += affected