>python -m timeit -s "import collections; d=collections.defaultdict(lambda: None); d['abc']=123; " "x=d['XXX']"
5000000 loops, best of 5: 34.3 nsec per loop

This benchmark is not a fair comparison: the 'XXX' key is created at the first access. In short, this benchmark measure the performance of a dict lookup:

>python -m timeit -s "d={'abc':123}" "x=d['abc']"
5000000 loops, best of 5: 33 nsec per loop