Unwanted behaviour from dict.fromkeys

Question

I\'d like to initialise a dictionary of sets (in Python 2.6) using dict.fromkeys, but the resulting structure behaves strangely. More specifically:

Answer 1

Because of this from the dictobject.c:

while (_PyDict_Next(seq, &pos, &key, &oldvalue, &hash))
{
            Py_INCREF(key);
            Py_INCREF(value);
            if (insertdict(mp, key, hash, value))
                return NULL;
}

The value is your "set([])", it is evaluated only once then their result object reference count is incremented and added to the dictionary, it doesn't evaluates it every time it adds into the dict.