Lists

Mon W1

Announcements

• Welcome to IDS-101-13: Thinking Machines!
• It's other first week of class!
• Today we're doing something interesting I hope
  • "Arithmetic is boring." -everyone except me
  • "Long division? I'm in college." -everyone except me
  • "Can I teach them something cool?" -Shouvik
  • "We don't have to be having fun for it to be fun." -me
• How about "data" - I hear "data" is cool.

Data

• Today's lecture brought to you by the University's "Strategic Plan"
• There are three "areas of focus":
  • Big data and human-centered computing
  • Democratic Institutions
  • Climate Change

Be sure to introduce yourselves!

Question #1

Whose values are reflected in the University's Strategic Goals?

• Think about a possible answer on your own
• Discuss your answers with the rest of the group
• Record a summary of each group’s discussion

Question #2

How can thinking machines help us explore the idea of "data"?

• Think about a possible answer on your own
• Discuss your answers with the rest of the group
• Record a summary of each group’s discussion

Python

• Recall we have thematically introduced annoyance to resolve in latter lectures.
• I found writing out this expression "annoying": triple_check = lambda a, b, c: print(a*a + b*b == c*c)
• Thinking machines are better at some things than I am, like:
  • Arithmetic
  • Doing the same task over and over.
• So I should find a way to ask the machine to do this for me.
  • I want a way to say "take these variables and do the same the same thing to all of them.
  • Python has my favorite way to do that of any programming language!
  • Those "things" could be information about electors... or whatever.

Tuple

• Tuples are the (one of the) ways Python solves this problem.
• Instead of saying, here are three variables "a", "b", and "c" a, b, c = 6, 8, 10
• We can make a variable for the whole triple, say "t". t = 6, 8, 10
• This, uh, does so happen to break "triple_check" --------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-10-267dfa60672e> in <cell line: 1>() ----> 1 triple_check(t) TypeError: triple_check() missing 2 required positional arguments: 'b' and 'c'

Question #3

Read the error message.
What do you think it means?
How might you fix (or try to fix) it?

• Think about a possible answer on your own
• Discuss your answers with the rest of the group
• Record a summary of each group’s discussion

List

• Okay so we have our triple: t = 6, 8, 10
• I always get nervous about this way of writing because to me it feels ambigious.
  • What would the following mean: b = x, y a, b = 1,2,3
• Here is another, more explicit, way to put multiple things together. t = [6, 8, 10]
• This forms a list, and I like using lists better because...
  • Visually, they are enclosed in square brackets "[]" which I find easy to see.
  • Lists have a nice feature - comprehension - that we can use.

Comprehension

• Now say we want to "check" this list t = [6, 8, 10]
• Previously we did every square individually triple_check = lambda a, b, c: print(a*a + b*b == c*c)
• List comprehension gives us a way to do more than just one arithmetic operation at a timesquares = [x*x for x in t]

Comprehension

• Exercise A.7 Write a function that prints a list with 7 added to all numbers in the list.
  • Consider the following: squares = [x*x for x in t]
  • What does this code do?
    • What is 'squares'?
    • What is 'x*x'?
    • What is 'for x'?
    • What is 'in t'?
  • Write a function, say "add_seven()"...

Question #4

What process do you use to understand code?

• Think about a possible answer on your own
• Discuss your answers with the rest of the group
• Record a summary of each group’s discussion

Indices

• Exercise A.8 Write a function prints the final element of a list.
  • Consider the following: conts = ['Africa', 'Americas', 'Antarctica', 'Eurasia', 'Oceania'] print(conts[1])
  • What does the 1 in this code do?
  • What happens if you change it to
    • Large values, like 400 or 400 ** 400?
    • Non-integer values, like 0.5?
    • Anything else?
  • Write a function, say "print_last()"...

Question #5

What are the uses and limitations of creativity in Python?

• Think about a possible answer on your own
• Discuss your answers with the rest of the group
• Record a summary of each group’s discussion

Homework

• Homework 2 Order of Operations
  • There is this arithmetic concept called "order of operations" sometimes called PEMDAS:
    • Parenthesis
    • Exponentiation
    • Multiplication/Division
    • Addition/Subtraction
  • Conduct a series of tests to determine whether Python follows PEMDAS rules or not.
  • You may make a copy of this Notebook and share it with me and anyone with whom you collaborate.
    • Give Shouvik and I edit permissions.
    • Due Fri @ 12 Noon (so we're able to discuss it in class)
    • You may only give your peers view or comment permissions.