A parameterless call to Python's `int` builtin returns zero

By Ed Wilson

A parameterless call to Python’s int builtin returns 0

The following test passes:

assert int() == 0

Which fits in with the notion from set theory that the numerical representation of nothing is 0. Unfortunately though calling int on python’s empty set does not return 0. The same goes for the float builtin.

This is useful for example to aggregate a collection of objects using a defaultdict. Here is a simple example of this:

import collections
import dataclasses
import random


@dataclasses.dataclass
class Item:
    id: str

my_items = [Item(id=id) for id in random.choices(["foo", "bar", "baz"], k=10)]
counts = collections.defaultdict(int)

for item in my_items:
    # Indexing `counts` for a non-present `id` will create a new
    # key with value 0, since `int` is used as the default factory. 
    counts[item.id] += 1