Question

Say you want to pass a dictionary of values to a function, or otherwise want to work with a short-lived dictionary that won’t be reused. There are two easy ways to do this:

Use the dict() function to create a dictionary:

foo.update(dict(bar=42, baz='qux'))

Use an anonymous dictionary:

foo.update({'bar': 42, 'baz': 'qux'})

Which do you prefer? Are there reasons other than personal style for choosing one over the other?

Answer 1

I prefer the anonymous dict option.

I don’t like the dict() option for the same reason I don’t like:

 i = int("1")

With the dict() option you’re needlessly calling a function which is adding overhead you don’t need:

>>> from timeit import Timer
>>> Timer("mydict = {'a' : 1, 'b' : 2, 'c' : 'three'}").timeit()
0.91826782454194589
>>> Timer("mydict = dict(a=1, b=2, c='three')").timeit()
1.9494664824719337