Composition & Closures — Series 2

Preview — 3 of 10 questions

What is the output of the following code?

javascript

from itertools import groupby

data = [("a", 1), ("a", 2), ("b", 3), ("b", 4)]
groups = list(groupby(data, key=lambda x: x[0]))

result = []
for key, group in groups:
    result.append((key, list(group)))
print(result)

A[('a', [('a', 1), ('a', 2)]), ('b', [('b', 3), ('b', 4)])]

B[('a', []), ('b', [])]

C[('a', [('a', 1), ('a', 2)]), ('b', [])] — only the last group ends up exhausted.

DTypeError: group object already consumed

What is the output of the following code?

javascript

def make_checkers():
    def is_even(n):
        if n == 0:
            return True
        return is_odd(n - 1)

    def is_odd(n):
        if n == 0:
            return False
        return is_even(n - 1)

    return is_even, is_odd

is_even, is_odd = make_checkers()
print(is_even(10))
print(is_odd(10))
print(is_even(7))

ATrue, True, False

BNameError: name 'is_odd' is not defined — is_even can't reference is_odd before it's been defined.

CRecursionError: maximum recursion depth exceeded

DTrue, False, False

What is the output of the following code?

javascript

cache = {}

def memoize(func):
    def wrapper(arg):
        if arg not in cache:
            cache[arg] = func(arg)
        return cache[arg]
    return wrapper

@memoize
def process(data):
    return sum(data)

print(process((1, 2, 3)))
process([1, 2, 3])

A6, then TypeError: cannot use 'list' as a dict key (unhashable type: 'list')

B6, then 6 — the cache silently converts the list to a tuple before checking membership.

CTypeError on the very first call already, since (1, 2, 3) and [1, 2, 3] can't both be used with the same cache.

D6, then None — a cache miss for an unhashable argument silently returns None instead of raising.

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