{} vs dict

gistfile1.py

In [1]: from timeit import timeit

In [2]: a = lambda: dict()

In [3]: b = lambda: {}

In [4]: n = 1000000

In [5]: [(timeit(a, number=n), timeit(b, number=n)) for x in range(10)]
Out[5]: 
[(0.18719196319580078, 0.0938410758972168),
 (0.16950392723083496, 0.09456491470336914),
 (0.1706409454345703, 0.09294795989990234),
 (0.16990113258361816, 0.09202790260314941),
 (0.16895294189453125, 0.09336018562316895),
 (0.1697380542755127, 0.09495186805725098),
 (0.1697099208831787, 0.09295296669006348),
 (0.16980290412902832, 0.09306979179382324),
 (0.1685340404510498, 0.09412407875061035),
 (0.17179489135742188, 0.09311914443969727)]