Readings and PS1

[winterthunder]

Hi everyone!

First, class business... I went poking around the website, and I found a suggested schedule for the problem sets. They actually correspond to the lectures, imagine that! Anyway, armed with this new info, I've made some tweaks to the problem set schedule.



PS2- 1/22
PS3- 2/5
PS4- 2/19
PS5- 3/5
PS6- 3/19
PS7- 3/26
PS8- 4/16
PS9- 4/23
PS10- 4/30
PS11- 5/14
PS12- 6/4



I also discovered that there are three quizzes associated with this course. So I'm putting the question to you all - do you want to do them?

Poll #2096 Quiz? What Quiz?

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View Respondents

I would like to include the quizzes in the course.

View Answers

Yeah, sure, extra practice is good.
7 (100.0%)

No way, I've got enough on my hands with the problem sets.
0 (0.0%)

If you would like to do the quizzes, how should we incorporate them?

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Add them on top of the lecture and reading in the week where they fit in the sylabus.
7 (100.0%)

Push the lectures back a week to make time for the quiz
0 (0.0%)

Some other idea which I'll tell you about in the comments
0 (0.0%)

Okay, that's out of the way, on to the readings.

I gotta say, this week kicked my ass, and these readings were right there with work and family issues, putting their prints on my bum. The wikibook chapters in particular just are not working for me. Is anyone else having that issue? My notes on those chapters are scattered with big red question marks and underlines with "What does this mean??" written off to the side. Part of this, I think, is that I really don't do numbers. I had to go look up the definition of a prime for the problem set...

Anyway, I've got some questions to toss out for discussion.

1- From the Data Structures reading, what are stacks and queues and why do we care about them? The reading just goes, 'This makes it easy to use lists in stacks and queues, whee!' (Or at least, that was my impression...)
2- From the same reading, why is it useful to be able to unpack a tuple?

Anyone else have questions for the class? This set of readings certainly provides fertile ground for questions. All of section 5.8 of the Data Structures had me going, "Bzuh?" And I just gave up on the wikibook...

Poll #2097 Who rocked problem set one?

Open to: Registered Users, detailed results viewable to: All, participants: 1

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I have...

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Knocked it out of the park.
1 (100.0%)

Struck out.
0 (0.0%)

There's still another at bat to go!
0 (0.0%)

I thought problem set one...

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Was easy peasy
0 (0.0%)

Was a pain, but achievable
1 (100.0%)

Was way too hard... when did we learn how to do this stuff, again?
0 (0.0%)

Now, aranthe has generously posted answers to some of the exercises in the readings. Anyone want to volunteer to do that for PS1?

Comments

[winterthunder]

Wait... when you unpack a tuple, you're assigning names to the data rather than pulling the data from the tuple? Wow, that makes so much more sense!

So for a stack and a queue... are these types of lists? If you add something to a list with a stack, does that limit you to only adding other items via stack?

[aranthe]

Wait... when you unpack a tuple, you're assigning names to the data rather than pulling the data from the tuple?

If I'm understanding your question correctly, yes: When you unpack a tuple, the tuple itself remains intact. Unpacking merely assigns the value of each element of the tuple to a name. This does not change the tuple in any way. If you do this...

# Create a tuple.
person = 'Doe', 'Jane', '01.17.80'

# Print the tuple.
print person

# Now, unpack it.
last, first, birth = person

# Print the unpacked variables
print last, first, birth

# Okay, let's make a change to the last name.
last = 'Mrs. John ' + last

# Now, print those variables again
print last, first, birth

# Now print the tuple again.
print person

...here's what the output looks like:

('Doe', 'Jane', '01.17.80')
Doe Jane 01.17.80
Mrs. John Doe Jane 01.17.80
('Doe', 'Jane', '01.17.80')

Line 1 is the tuple. Line 2 shows the three variables after they are unpacked. Line 3 shows the three variables with the change to last. Line 4 shows that the tuple remains unchanged.

So for a stack and a queue... are these types of lists? If you add something to a list with a stack, does that limit you to only adding other items via stack?

Let's see if I can find a better way to put it: A list is just a sequence or collection of data. Without context, it isn't a stack or a queue.

"Stack" and "queue" are (unnecessarily confusing) terms programmers use to tell other programmers what order they are using to add/remove elements to and from the list. If I'm treating the list as a stack, I remove the last item first. If I'm treating it as a queue, I remove the first item first.

It would make a lot more sense if people used the words in their verb form: "I'm stacking this list" or "I'm queuing this list" because it has to do with the way you treat a list, not with anything that is inherent in the list itself. Does this make more sense?

To answer your second question, no, there are no technical constraints to prevent you switching back and forth between the two behaviors. There may be good logical reasons to treat the data in one way or the other, but that's the sort of thing you have to determine when you're planning a program.

BTW, here's a way to keep the terms straight in your head: For stack, picture a stack of books. Unless you want a real mess, it's best you remove the last (topmost) item and work your way down, right? For a queue, think about a customers in a checkout queue: The first one to arrive at the cashier gets checked out first (unless you want a riot).

[winterthunder]

So in the unpacked tuple, when you modify "last", it's like you're ... appending information onto just that piece. I'm a very visual person, so this might make no sense, but this is the image I have: the tuple as a shark and the change to the unpacked tuple as a remora. The remora comes up and attaches to, let's say the shark's fin, and therefore becomes something that has to be considered with regards to drag and velocity, but it doesn't intrinsically change the fin of the shark and if you tore the remora off, the shark fin would still be the same.

Stacks as books and queues as a line of customers... got it!

[aranthe]

I get the visualization thing. I do it myself. :-) About the shark and remora analogy, just remember that the remora isn't attached to the shark at all. Here's another way to visualize the concept which works for any type of change, not just for appending:

Suppose you create a bouquet which contains a white carnation, a red rose, a yellow tulip and an orange lily. (Not very likely, but...) You tie a tag around the bouquet and label it bouquet (the tuple). Also, each flower has its own tag: bouquet[0], bouquet[1], etc. These are the elements of the tuple.

When you unpack the tuple, you add a second tag to each of those flowers. Maybe you name them by variety carnation, rose, etc.

Now, suppose you'd prefer a purple carnation and decide to use the old food coloring trick to change the color of the carnation. Whoops! Python says that you can't change the tuple (bouquet) or any of its parts. Instead, you have to get another white carnation and dye it. When you do that, Python moves the carnation tag from the white carnation in the tuple bouquet and gives it to the purple carnation. The white carnation is still bouquet[0], but the carnation tag is now around the purple carnation.

In other words, the tuple and its elements are "frozen." Using the unpacked names, you can make changes, but when you do, the changed data is completely independent of the original.

[winterthunder]

Ah, ok, that makes sense! Thanks! :)

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[(Anonymous)]

This is the prfceet way to break down this information.

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[(Anonymous)]

That's really tihnknig out of the box. Thanks!

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[(Anonymous)]

This arctile went ahead and made my day.

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[(Anonymous)]

Ooops, you are right. I agree with you. Yes, if he cared about Victoria's welfare he would stop pesneritg her. And yes, it is all about his need to be successful at getting people to smile. I don't think that stalking is romantic or that women should smile for men on command.When I posted this, I'd forgotten about the bit in the clip between him and Victoria. The bit that stood out for me is our shared need for validation. I just love the idea of people queuing up to be validated. It makes me laugh and makes me feel stupid. So, it was lazy on my part! A lazy feminist with no attention to detail, that's me. Thanks for watching it properly and commenting much appreciated.

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[(Anonymous)]

Shoot, so that's that one spuposes.