Classwork 2

Python Fundamentals

Question 1. Python Operations and Basic Data Structures

(a) Arithmetic with Powers and Parentheses

Using Python operations only, calculate below: \[\frac{2^5}{7 \cdot (4 - 2^3)}\]

Show answer

# NOTE: In Python, exponentiation is ** (not ^)

result = (2**5) / (7 * (4 - 2**3))

• -1.1428571428571428 (which is exactly -8/7)

(b) Adding Mixed Types by Converting Strings

Given:

data = [10, 2.5, "3"]

Using Python only, calculate 10 + 2.5 + 3

Show answer

total = data[0] + data[1] + float(data[2])

(c) Computing a Weighted Exam Score with max()

Given:

exam_score = {"Midterm": 78, "Final": 92}

Compute the Total Exam Score:

\[ \begin{align} \text{(Total Exam Score)} = \max\{ &0.50\times \text{(Midterm)} + 0.50\times \text{(Final)},\\ &0.33\times \text{(Midterm)} + 0.67\times \text{(Final)} \} \end{align} \]

Show answer

simple_avg = 0.50 * exam_score["Midterm"] + 0.50 * exam_score["Final"]
weighted_avg = 0.33 * exam_score["Midterm"] + 0.67 * exam_score["Final"]

total_exam_score = max(simple_avg, weighted_avg)

Question 2. Boolean Expressions and Logic

For each expression below, what is the value of the expression? Explain thoroughly.

(a) Comparing Different Data Types (int vs str)

20 == '20'

Show answer

• False
• Why?
  • 20 is an integer, but ‘20’ is a string.
  • Different types are not equal.

(b) Logical Operators with Comparisons (or)

x = 4.0
y = .5

x < y or 3*y < x

Show answer

• True
• Why?
  • x < y → 4.0 < 0.5 → False
  • 3*y < x → 1.5 < 4.0 → True
  • False or True → True

Question 3. Conditional Statements (if / elif / else)

(a) Tracing an if-Chain (Membership and Thresholds)

What will the following code print? (Answer without running it.)

status = "Gold"
cart_total = 92.5

free_shipping_levels = ["Gold", "Platinum"]

if status in free_shipping_levels:
    shipping = 0
    msg = f"Status: {status} → Free shipping! Total = ${cart_total}"
elif cart_total >= 100:
    shipping = 0
    msg = f"Spend threshold met → Free shipping! Total = ${cart_total}"
else:
    shipping = 7.99
    msg = f"Status: {status}, Total = ${cart_total} → Shipping = ${shipping}"

print(msg)

Show answer

What will it print?

• status is "Gold"
• "Gold" in ["Gold", "Platinum"] is True, so the first if-branch runs.

So it prints:

Status: Gold → Free shipping! Total = $92.5

(b) Fill-in-the-Blanks: Writing an if-elif-else Chain

• Fill in the blanks:
  • If name is "Geneseo" and score >= 90 → print "Geneseo high score"
  • Else if score >= 90 → print "High score"
  • Else → print "Try again"

name = "Geneseo"
score = 88

# Fill in the blanks
if ______________________________:
    print("Geneseo high score")
elif ____________________________:
    print("High score")
else:
    print("Try again")

Show answer

name = "Geneseo"
score = 88

if name == "Geneseo" and score >= 90:
    print("Geneseo high score")
elif score >= 90:
    print("High score")
else:
    print("Try again")

Question 4. List Slicing and String Slicing

(a) Predicting Output from List Slices

What will the following code print? (Do not run it—reason it out.)

nums = [10, 20, 30, 40, 50, 60, 70]

print(nums[2:6])
print(nums[:4])
print(nums[::2])
print(nums[-4:-1])

Show answer

[30, 40, 50, 60]
[10, 20, 30, 40]
[10, 30, 50, 70]
[40, 50, 60]

(b) Extracting Numbers from Strings with Slicing

fare = "$10.00"
tip = "2.00$"
tax = "$ 0.80"

Write a Python code that uses slicing and the print() function to print out the following message:

The total trip cost is: $12.80

Show answer

fare_num = float(fare[1:])     # "10.00"
tip_num  = float(tip[:-1])     # "2.00"
tax_num  = float(tax[2:])      # "0.80"

total = fare_num + tip_num + tax_num

print(f"The total trip cost is: ${total:.2f}")

Question 5. Finding the Maximum Value in a List

list_variable = [100, 144, 169, 1000, 8]

Write a Python code that uses print() and max() functions to print out the largest value in the list, list_variable, as follows:

The largest value in the list is: 1000

Show answer

list_variable = [100, 144, 169, 1000, 8]

largest = max(list_variable)
print(f"The largest value in the list is: {largest}")

Question 6. Looping Through a List (while vs for)

vals = [3, 2, 1, 0]

(a) while loop

Use a while loop to print each value of the list [3, 2, 1, 0], one at a time.

Show answer

vals = [3, 2, 1, 0]
counter = 0

while counter < len(vals):
  print(vals[counter])
  counter += 1

(b) for loop

Use a for loop to print each value of the list [3, 2, 1, 0], one at a time.

Show answer

vals = [3, 2, 1, 0]

for val in vals:
  print(val)

Question 7. Loop Control with Comparisons and Early Exit

Start with guess_me = 7 and number = 1.

guess_me = 7
number = 1

(a) while loop

Write a while loop that keeps running until you break:

• If number < guess_me, print "too low" and then increment number by 1.
• If number == guess_me, print "found it!" and then break.
• If number > guess_me, print "oops" and then break.

Show answer

guess_me = 7
number = 1

while True:
  if number < guess_me:
    print("too low")
    number += 1
  elif number == guess_me:
    print("found it!")
    break
  else:
    print("oops")
    break

(b) for loop

Write the same logic using a for loop that tries values from 1 to 10:

• If the current value is less than guess_me, print "too low".
• If it equals guess_me, print "found it!" and then break.
• If it is greater than guess_me, print "oops" and then break.

Show answer

guess_me = 7
number = 1

for num in range(1,11):
  if num < guess_me:
    print("too low")
  elif num == guess_me:
    print("found it!")
    break
  else:
    print("oops")
    break

Question 8. Comprehensions & Modifying Collections

(a) List & Dictionary Comprehensions

Given a list of three dictionaries:

lst_students = [
    {"name": "Ava",  "major": "DANL", "score": 91},
    {"name": "Ben",  "major": "ECON", "score": 84},
    {"name": "Cara", "major": "DANL", "score": 76},
]

1. Use a list comprehension to create danl_names, the names of students whose major is "DANL".
   
2. Use a dictionary comprehension to create danl_scores mapping name → score for only "DANL" students.

Show answer

# (a) Comprehensions

# list comprehension
danl_names = [d["name"] for d in lst_students if d["major"] == "DANL"]

# dict comprehension
danl_scores = {d["name"]: d["score"] for d in lst_students if d["major"] == "DANL"}

(b) Modifying Lists & Dictionaries

1. Modify nums using .append() to add 99.

nums = [2, 5, 2, 8]

2. Modify grades using .update() to (i) add "Cara": 76 and (ii) change "Ben" to 90.

grades = {"Ava": 91, "Ben": 84}

Show answer

# (b) Modifying lists & dictionaries

nums.append(99)

grades.update({"Cara": 76, "Ben": 90})

Question 9. Error Handling with try–except

You are given a variable value that stores a string:

value = "$320"

Write a Python program that does the following:

1. Attempt to convert value into a floating-point number using float().
2. If the conversion is successful, print:
   You entered:
3. If the conversion fails (for example, because the string is not a valid number), print:
   That’s not a valid number!

Your program must use a try–except block to handle the potential error gracefully.

Show answer

Question 10. Imports and Library Setup (pandas + selenium)

(a) Importing a Library with an Alias

Import the pandas library as pd.

Show answer

import pandas as pd

(b) Installing an External Library

Install the selenium library.

Show answer

!pip install selenium

(c) Importing from a Submodule

From selenium, import the function webdriver.

Show answer

from selenium import webdriver

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