Skip to content

Oct 21: Practice quiz 4; Loops and Modules

Learning Objectives

After today's class, you should be able to:

  • Explain when to use a for loop versus a while loop.
  • Predict the output of code segments with a for loop.
  • Explain the purpose of if name == "main".

Announcements

  • Project 1, due tonight
  • Today is the last day to drop the course. Recall a B- is required to take to CS159 and only two attempts are allowed for CS149

Practice Quiz 4

  • Two portions to the quiz: written and coding
  • Log in as student
  • Start exam recording
  • Log in to Canvas only
  • Raise your hand when complete with Canvas written portion
  • Open Thonny for coding portion only
  • Submit code through Canvas (will go to Gradescope)
  • Log out when finished

For vs While loops

Exercise

Rewrite the following:

Rewrite coin_toss.py using a while loop 

"""Simulate tossing a coin one million times."""

import random

heads = 0
tails = 0
times = 1000000

for _ in range(times):
    if random.random() < 0.5:
        heads += 1
    else:
        tails += 1

heads = round(heads / times * 100, 2)
tails = round(tails / times * 100, 2)

print(f"Head: {heads}%, Tail: {tails}%")
Rewrite guess_numbers.py using a for loop 
"""Play a random number guessing game."""

import random

print("Guess my number!")
number = random.randint(1, 100)

guess = 0
while guess != number:
    guess = int(input("Guess: "))
    if guess > number:
        print("Too high!")
    elif guess < number:
        print("Too low!")

print("You got it!")

Tracing For Loops

For each for loop:

  • Predict the output/behavior by hand on paper.
  • Check your answer using Thonny's debugger.

For-1

for row in range(10):
    print(row, end="\t")
    print("#" * row)

For-2

cities = ["boise", "omaha", "tulsa", "utica"]
result = []
for city in cities:
    result.append(city.upper())
print(result)

For-3

word = "onomatopoeia"
locs = []
for i in range(len(word)):
    if word[i] in ("a", "e", "i", "o", "u"):
        locs.append(i)
print("Locations:", locs)

For-4

count = 0
prev = 0
words = ["Book", "Car", "City", "Dog", "Enough", "Friend", "House"]
for w in words:
    if len(w) < prev:
        count += 1
    prev = len(w)
print("Count is", count)

For-5

name = "James Madison University"
words = name.split()
acronym = ""
for word in words:
    letter = word[0]
    print(letter, "is for", word)
    acronym += letter
print(acronym)

For-6

index = None
word = "Mississippi"
for i in range(len(word) - 1):
    if word[i] == word[i + 1]:
        index = i
print("Index is", index)

Tracing Modules

  • Value of the built-in variable __name__
    • When running move.py
    • When running stop.py
  • Purpose of if __name__ == "__main__":

move.py 

import random

def angle():
    number = random.randint(-90, 90)
    return number

print("in move: __name__ ==", __name__)
print("will always execute: angle ==", angle())

if __name__ == "__main__":
    print("only if True: angle ==", angle())
stop.py 
import move

print("in stop: __name__ ==", __name__)
print("from module: angle ==", move.angle())