Sized collections¶

Sized[container, expr] validates the container and then checks that its length matches the expression. Expressions can be constants, symbols, or simple arithmetic such as "n + 1".

When a symbol is first seen, it is bound to the observed length. Later uses of the same symbol must match.

Example¶

from depend import Context, Sized, ValidationError, checked, validate

annotation = Sized[list[int], "n"]
ctx = Context(path=("values",))

assert validate([1, 2, 3], annotation, ctx) == [1, 2, 3]
assert ctx.symbols["n"] == 3

@checked
def dot(a: Sized[list[int], "n"], b: Sized[list[int], "n"]) -> int:
    return sum(a) + sum(b)

assert dot([1, 2], [3, 4]) == 10

try:
    dot([1, 2], [3])
except ValidationError:
    pass