Interfaces

Questions 1 to 5 of 6

1. 1. According to the interface design lesson, what should you look at first when you design an interface?

   The attributes that the implementing class storesThe number of methods the old version of the class hadThe caller, meaning the code that uses the object and what it actually needs from itThe database table that the data will eventually be saved into
2. 2. The TestStorage class in the fat interface example writes only save and load. What happens when the code runs TestStorage()?

   It works, because no caller calls compactTypeError, because Python refuses to create an object while any abstract method is still unwrittenIt raises AttributeError the first time save is calledIt runs, and calling compact() returns None
3. 3. Match each term from the interface design lesson to its meaning.

   Choose the matching item for each row.

   CallerChoose…A method name with no body that every subclass must writeA fake object that stands in for the real oneAn interface with many methods, most of which some implementers never needThe code that uses an objectFat interfaceChoose…A method name with no body that every subclass must writeA fake object that stands in for the real oneAn interface with many methods, most of which some implementers never needThe code that uses an objectAbstract methodChoose…A method name with no body that every subclass must writeA fake object that stands in for the real oneAn interface with many methods, most of which some implementers never needThe code that uses an objectTest doubleChoose…A method name with no body that every subclass must writeA fake object that stands in for the real oneAn interface with many methods, most of which some implementers never needThe code that uses an object
4. 4. Statement: a method in an abstract base class that no caller uses can stay, because nothing runs it and so it cannot cause a bug.

   True, because a method that nothing calls cannot break any codeFalse, because every subclass must still write the method, even though nothing calls itFalse, because Python rejects any abstract method that has no callerTrue, because Python removes unused abstract methods automatically
5. 5. What does this program print? ``python class Rule: def __init__(self, test): self._test = test def passes(self, n): return self._test(n) def __and__(self, other): return Rule(lambda n: self.passes(n) and other.passes(n)) def __invert__(self): return Rule(lambda n: not self.passes(n)) big = Rule(lambda n: n >= 10) even = Rule(lambda n: n % 2 == 0) for n in [4, 11, 12, 15]: print(n, (big & even).passes(n), (~big).passes(n)) ``

   4 False False 11 False False 12 True True 15 False False4 False True 11 False True 12 True False 15 False True4 False True 11 False False 12 True False 15 False False4 True False 11 True False 12 True False 15 True False