Slides 3: Types

Exercise 3.b.1

What data type would you use to represent the following?

1. A person's first name
2. The first names of all the students in this course
3. The Quiz 1 scores for each of those students
4. A person's birth date (year, month, and day)
5. An address book entry (name, email, major, …)
6. A person's age in years
7. A person's height in meters

Write an example assignment statement for each.

a. str
b. List[str]
c. List[int] or Dict[str, int]
d. Tuple[int, int, int]
e. {'name': str, 'email': str, 'major': str, ...}
f. int
g. float

Example Assignment Statements

a = "Alice"
b = ["Alice", "Bob", "Charlie"]
c = [90, 85, 95]
# or: c = {"Alice": 90, "Bob": 85, "Charlie": 95}
d = (2000, 1, 1)
e = {"name": "Alice", "email": "ak12@calvin.edu", "major": "Biology"}
f = 20
g = 1.75

Assume x = 'alphabet' How could you get the b?

• x(6)
• x[6]
• x[5]
• x(-4)
• x{-3}

Exercise 3.b.2

Generally speaking, one can view strings as lists of characters, but …

Exercise 3.b.2.a

Can you predict what the code segments do to the value of x and explain why they work that way?

x = '12'
x[1] = '3'

x = [1, 2]
x[1] = 3

Exercise 3.b.2.b

Can you predict what the code segments do to the values of x and y and explain why they work that way?

x = 'hi'
y = x
x.upper()

x = ['h', 'i']
y = x
x[1] = 'o'

Exercise 3.b.2.c

How would similar code segments work on integers, floats, dictionaries and tuples?

Name-Object Diagrams

Draw the name-object diagram for the following code:

s = "bht"
s.upper()
print(s)

Note that the upper() method creates a string with all uppercase letters.

Strings are immutable. The upper() method returns a new string.

Name-Object Diagrams with Lists

a = [3, 2, 1]
b = a
b[0] = 50
c = b + a
print(c)

• [50, 2, 1, 3, 2, 1]
• [50, 2, 1, 50, 2, 1]
• [100, 4, 2]
• [53, 4, 2]
• None of the above

Answers reflect misconceptions:

1. thinks that b=a copies a
2. (correct)
3. thinks that + operates elementwise, but got correct values
4. thinks that + operates elementwise, also thought b=a copies a

Name-Object Diagrams with Lists, 2

a = [3, 2, 1]
b = a.copy()
b[0] = 50
c = b + a
print(c)

• [50, 2, 1, 3, 2, 1]
• [50, 2, 1, 50, 2, 1]
• [100, 4, 2]
• [53, 4, 2]
• None of the above

Answers reflect misconceptions:

1. thinks that b=a copies a
2. (correct)
3. thinks that + operates elementwise, but got correct values
4. thinks that + operates elementwise, also thought b=a copies a

Which makes most sense to you?

1. “[Technology is] essentially amoral, a thing apart from values, an instrument which can be used for good or ill.” — R. Buchanan, Technology and Social Progress, 1965.

2. “Embedded in every tool is an ideological bias, a predisposition to construct the world as one thing rather than another, to value one thing over another, to amplify one sense or skill or attitude more loudly than another.” — N. Postman, Technopoly: The Surrender of Culture to Technology, 1992.

3. “…automated machine processes not only know our behavior but also shape our behavior… the goal now is to automate us…through the automated medium of an increasingly ubiquitous computational architecture of”smart” devices, things, and spaces.” S. Zuboff, The Age of Surveillance Capitalism, 2019, p.8