Patterns and custom keys

Questions 1 to 5 of 8

1. 1. A one-dict check that only goes from each letter of badc to the letter in the same position of baba returns True. Why is that wrong?

   Both strings have length 4, so the check stops before it compares any lettersTwo different letters on the left, b and d, both end up pointing at the same letter b, and a one-way check never looks in that directionbadc has no repeated letters, so the check cannot tell the strings apartThe check uses == on single characters, which always returns True for letters
2. 2. What does ''.split(' ') return in Python?

   An empty list, []NoneA list with two empty strings, ['', '']A list with one empty string, ['']
3. 3. A student wrote this class and then tried to add a Point to a set. What is the bug? ``python class Point: def __init__(self, x, y): self.x = x self.y = y def __eq__(self, other): return isinstance(other, Point) and self.x == other.x and self.y == other.y points = set() points.add(Point(3, 4)) ``

   The attributes x and y must be listed in __slots__, or the set cannot store themDefining __eq__ without __hash__ sets the class's __hash__ to None, so add raises TypeError: cannot use 'Point' as a set element (unhashable type: 'Point')The isinstance check is not allowed inside __eq__The constructor must be a @staticmethod, so that the set can call it
4. 4. The check below returns False for the pattern abba and the sentence dog cat cat dog, which is wrong. What is the bug? ``python mapped = letter_to_word.get(letter) if mapped is None: letter_to_word[letter] = word elif mapped is not word: return False ``

   mapped should be an int, because the words are numberedThe dict should be a set, because split returns each word only onceThe elif should be a while, so the loop runs again for the same letteris not compares object identity, so two equal words at different positions in one sentence can count as different. The check should use !=, which compares the text
5. 5. A student says the strings 'ab' and 'aa' are isomorphic, which means each letter maps to one letter and no two letters share a partner. Is that true?

   False, because a and b on the left both map to a on the right, which breaks the one-to-one ruleTrue, because each letter of ab appears only once, so no letter repeats