Chapter 9: Mappings & Sets (Review Questions)¶

The questions below assume that you have read the first , second , and third part of Chapter 9.

Be concise in your answers! Most questions can be answered in one sentence.

Essay Questions¶

Q1: dict objects are well-suited to model discrete mathematical functions and to approximate continuous ones. What property of dictionaries is the basis for that claim, and how does it relate to functions in the mathematical sense?

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Q2: Explain why hash tables are a trade-off between computational speed and memory usage!

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Q3: The dict type is an iterable that contains a finite number of key-value pairs. Despite that, why is it not considered a sequence?

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Q4: Whereas key look-ups in a dict object run in so-called constant time (i.e., extremely fast), that does not hold for reverse look-ups. Why is that?

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Q5: Why is it conceptually correct that the Python core developers do not implement slicing with the [] operator for dict objects?

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Q6: Memoization is an essential concept to know to solve problems in the real world. Together with the idea of recursion, it enables us to solve problems in a "backwards" fashion effectively.

Compare the recursive formulation of fibonacci() in Chapter 9 , the "Easy at second Glance" example, with the iterative version in Chapter 4 , the "Hard at first Glance" example!

How are they similar and how do they differ? Also consider how the flow of execution behaves when the functions are being executed.

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Q7: How are the set and the dict types related? How could we use the latter to mimic the former?

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True / False Questions¶

Motivate your answer with one short sentence!

Q8: We may not put dict objects inside other dict objects because they are mutable.

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Q9: Mutable objects (e.g., list) may generally not be used as keys in a dict object. However, if we collect, for example, list objects in a tuple object, the composite object becomes hashable.

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Q10: Mutability of a dict object works until the underlying hash table becomes too crowded. Then, we cannot insert any items any more making the dict object effectively immutable. Luckily, that almost never happens in practice.

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Q11: A dict object's .update() method only inserts key-value pairs whose key is not yet in the dict object. So, it does not overwrite anything.

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Q12: The set type is both a mapping and a sequence.

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