differences between “d = dict()” and “d = {}”

Question

$ python2.7 -m timeit \'d={}\'
10000000 loops, best of 3: 0.0331 usec per loop
$ python2.7 -m timeit \'d=dict()\'
1000000 loops, best of 3: 0.19 usec per loop
         


        

Answer 1

Doug Hellmann wrote up an exhaustive comparison of the performance difference.

tl;dr

With CPython 2.7, using dict() to create dictionaries takes up to 6 times longer and involves more memory allocation operations than the literal syntax. Use {} to create dictionaries, especially if you are pre-populating them, unless the literal syntax does not work for your case.