from functools import wraps
COUNTER = 0

def trace(fn):

    @wraps(fn)
    def wrapper(*a, **kw):
        global COUNTER
        COUNTER += 1
        return fn(*a, **kw)
    return wrapper

@trace
def factorial(n: int) -> int:
    if n < 0:
        raise ValueError('negative')
    return 1 if n <= 1 else n * factorial(n - 1)

def squares(limit):
    return [x * x for x in range(limit) if x % 2 == 0]

def gen_pairs(seq):
    for i, v in enumerate(seq):
        yield (i, v)

def make_adder(by=1):

    def add(x, *, scale=1):
        return (x + by) * scale
    return add

def categorize(n):
    match n:
        case 0:
            return 'zero'
        case x if x < 0:
            return 'negative'
        case _:
            return 'positive'

def run() -> None:
    print('factorials:', [factorial(i) for i in range(7)])
    print('squares:', squares(10))
    print('pairs:', list(gen_pairs('abcd')))
    add5 = make_adder(5)
    print('adder:', add5(3, scale=2))
    print('category:', [categorize(x) for x in (-1, 0, 7)])
    if (n := sum(squares(8))) > 100:
        print('walrus-large:', n)
    else:
        print('walrus-small:', n)
    try:
        factorial(-1)
    except ValueError as e:
        print('caught:', str(e))
    print('counter:', COUNTER)
if __name__ == '__main__':
    run()