Dictionary key/value loops

items() borrows a dictionary in insertion order. It works directly in loops and comprehensions, without allocating item tuples or a snapshot. Keys and values are shared references. Borrow the dictionary exclusively, (&mut counts).items(), to update every value in place; keys stay shared.

def main() -> Result[(), AllocError | IoError | OverflowError[i64]]:
    mut counts = {"apple": 2, "pear": 3}?
    for fruit, count in (&mut counts).items():
        *count += 1
    for fruit, count in counts.items():
        print(fruit)?
        print(count)?
    for a, b in [(1, 2), (3, 4)]?:
        print(a + b)?
    Ok(())

apple
3
pear
4
3
7

(&mut counts).values() lends only the values. Neither loop looks a key up or copies a value, so they suit values that cannot be copied. The dictionary cannot grow, shrink, or be read through another path during a mutable loop. A shared items() or values() view can be bound to a name and reused; a mutable one is used directly as the loop source. See updating every value for the full contract.