Chapter 9, dictionary order as of Python 3.7 no longer unpredictable

[tom-price]

I noticed an inaccuracy due to a change in python 3.7 that, to my understanding, made it a language feature that dictionaries are ordered by insertion order.

The order of the key-value pairs is not the same. In fact, if you type the same example on your computer, you might get a different result. In general, the order of items in a dictionary is unpredictable.

This means one of the questions in the chapter 9 quiz on Coursera is now ambiguous and based on which version of Python 3 you're using.

[csev]

Thanks - I will keep this open. Someday we will redo everything (book, slides, videos) for use with a later version of Python and catch this. I will just hold the issue open as a reminder.

[csev]

Tom - they day has finally come. I just finished a major redo of Chapter 9 and all the associated lectures. Feel free to take a look, review and comment - https://do1.dr-chuck.com/pythonlearn/EN_us/pythonlearn.pdf (sorry this too way too long)

[tom-price]

Wonderful, congratulations on completing this work! I did take a look through chapter 9 (and the rest as a refresher).

A mistake I remember first making when starting with Python, and was reminded of by the start of chapter 9, was the distinction between:

type({})
type({'a'})

I expected {} to create an empty set not an empty dict as I was thinking about it like []. It might be worth mentioning set's use of curly brackets to help prevent future confusion when learners come across sets.

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I hate to say this on the heels of the completion of such a task, but have you considered adding a chapter between 14 and 15 mentioning dataclasses introduced in 3.7? I make quite heavy use of them now especially as I can define derived @property and set defaults.

Examples re-imprementing the classes in chapter 14 might be quite instructive.

from dataclasses import dataclass


@dataclass
class PartyAnimal:
    name: str
    x: int = 0

    def __post_init__(self):
        print(self.name, 'constructed')

    def party(self):
        self.x += 1
        print(self.name, "party count", self.x)

    def __del__(self):
        print(self.name, 'destructed', self.x)


class CricketFan(PartyAnimal):
    points: int = 0

    def six(self):
        self.points += 6
        self.party()
        print(self.name, "points", self.points)

NamedTuples also underwent some changes but to me seem to have stabilized and there may be benefits in contrasting the two and mentioning any differences between typing.NamedTuple and collections.namedtuple.