Hackerrank Collections and Data Structures 4

Question 1

What is the primary use case for `collections.ChainMap` compared to merging dicts with `{**d1, **d2}`?

Accepted Answer

ChainMap creates a live view that reflects changes to the underlying dicts

Answer

ChainMap holds references to the original dicts, so mutations to them are reflected in the ChainMap, unlike a merged copy.

Question 2

When using `defaultdict(int)`, what is the default value assigned to a newly accessed missing key?

Accepted Answer

0

Answer

int() called with no arguments returns 0, so defaultdict(int) initializes missing keys to 0.

Question 3

Which method would you use to get all elements from a Counter, including repeats, as an iterator?

Accepted Answer

counter.elements()

Answer

`elements()` returns an iterator yielding each element repeated as many times as its count.

Question 4

What happens if you create a `namedtuple` field name that starts with an underscore?

Accepted Answer

Raises a ValueError unless rename=True is passed

Answer

Field names starting with underscore are invalid; passing rename=True auto-renames them to positional names like _0, _1.

Question 5

How do you add a new child scope to an existing `ChainMap` for temporary overrides?

Accepted Answer

chainmap.new_child(new_dict)

Answer

`new_child(m)` creates a new ChainMap with m as the first map, making it the highest-priority scope.

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