Is it possible to give a python dict an initial capacity (and is it useful)

Question

I am filling a python dict with around 10,000,000 items. My understanding of dict (or hashtables) is that when too much elements get in them, the need to resize, an operatio

Answer 1

Yes you can and here is a solution I found in another person's question that is related to yours too:

d = {}
for i in xrange(4000000):
d[i] = None
# 722ms

d = dict(itertools.izip(xrange(4000000), itertools.repeat(None)))
# 634ms

dict.fromkeys(xrange(4000000))
# 558ms

s = set(xrange(4000000))
dict.fromkeys(s)
# Not including set construction 353ms

those are different ways to initialize a dictionary with a certain size.