python - Why does put() not work when used with indexed element in Query? -

i have issue put() not appear work if access model class indexed member of query directly; however, when explicitly extract class query seems work fine. why this?

this code works:

class record:    field = db.stringproperty()  rs = record.all().filter('name = ', name_str) if rs.count() == 1:    # assume 1 record in return...    r = rs[0]    r.field = some_value    r.put() 

and code doesn't (and not raise errors)

class record:    field = db.stringproperty()  rs = record.all().filter('name = ', name_str) if rs.count() == 1:    # assume 1 record in return...    rs[0].field = some_value    rs[0].put() 

every time index query this, performs query on again, fetches relevant result, decodes it, , returns you. in second snippet, modify 1 instance of entity, discard it, fetch , store (unmodified) second copy.

generally, should avoid indexing queries - call .get() or .fetch() instead.

for same reason, should avoid using .count() possible, since requires running query. if want 1 result, call .get(); if need more, call .fetch() , count number of results returned.