Trade-off in Python dictionary key types

Question

Say, I'm going to construct a probably large dictionary in Python 3 for in-memory operations. The dictionary keys are integers, but I'm going to read them from a file as string at first.

As far as storage and retrieval are concerned, I wonder if it matters whether I store the dictionary keys as integers themselves, or as strings.
In other words, would leaving them as integers help with hashing?

Answer 1

Dicts are fast but can be heavy on the memory. Normally it shouldn't be a problem but you will only know when you test. I would advise to first test 1.000 lines, 10.000 lines and so on and have a look on the memory footprint.

If you run out of memory and your data structure allows it maybe try using named tuples.

EmployeeRecord = namedtuple('EmployeeRecord', 'name, age, title, department, paygrade')
import csv
for emp in map(EmployeeRecord._make, csv.reader(open("employees.csv", "rb"))):
    print(emp.name, emp.title)

(Example taken from the link)

If you have ascending integers you could also try to get more fancy by using the array module.

Answer 2

Actually the string hashing is rather efficient in Python 3. I expected this to has the opposite outcome:

>>> timeit('d["1"];d["4"]', setup='d = {"1": 1, "4": 4}')
0.05167865302064456
>>> timeit('d[1];d[4]', setup='d = {1: 1, 4: 4}')
0.06110116100171581