Day 7: Strings! and midterm 1 exam practice

CMSC 201: Strings! And some exam practice

HW3

HW3 questions? Still due Friday 2024-09-27 at 11:59:59 PM :)

Midterm

Midterm #1 is October 9th for M/W October 10th for Tu/Th! There is no make-up time! Please don't miss it :(! I have no power to give you make-up times. TAs will be in the room, administering the test.

Reminder: If you have SDS accomodations (e.g., extra time or reduced distractions), please book that room and let them know you plan to take the test there! The room here will be very quiet though, so there won't be many auditory distractions.

"Fun": wargames

"Wargames" are online, long-running computer "competitions" (but really just some fun activities). They usually center around some specific technology (like Linux, or websites).

Overthewire's bandit wargame has been running forever, and is focused on using Linux :)! Each level is based on learning some skill. Let's briefly check it out: Bandit OverTheWire wargame.

Who cares (about string manipulations)?

Let's do censorship! :) Taking a string input, remove all undesirable words and replace them with our own! We are employed by the banana empire, on a mission to destroy all apple-related messages and spread the good word of the banana.

Strings

Strings in python are immutable! This means they are "passed by value". Or at least, they look like they're passed by value. You can not change them like lists (lists are mutable)!

Strings! Methods that operate on strings:

There's also functions that can take strings as an input:

These all RETURN a modified string, they do not modify the string in place. Strings are immutable in Python.

Challenge: Ask for a comma-delimited list of the places that make up the DMV. Keep asking until they get them all. When they do, print them all back.

places_list = ["dc","virginia","maryland"]
correct_list = []

while len(places_list) > 0:
    user_input = input("Give place name: ").lower()
    user_list = user_input.split(",")
    for entry in user_list:
        if entry in places_list:
            print("Correct!", entry)
            places_list.remove(entry)
            correct_list.append(entry)

print("Cool!", correct_list)

You can iterate through characters of a string, just like elements of a list.

place_name = "Maryland"
for letter in place_name:
    print(letter)

You can also do slices and indexing and all that good stuff.

place_name = "Maryland"
print(place_name[:4]) # "Mary"
print(place_name[3]) # y
print(place_name[2:5]) # "ryl"
print(place_name[100]) # IndexError: string index out of range
print(place_name[2:10000000000000]) # Why python?! Slices have no bounds limit, but indexing does

But it's not a list! Strings are immutable in Python! (They are very mutable in C, C++, Go...)

place_name = "Maryland"
place_name[0] = "B" # Fails!
# Outputs: TypeError: 'str' object does not support item assignment

Challenge: Alternate capital and lower letters of a given string ("computer science --> cOmPuTeR ScIeNcE").

user_sentence = input("Give me string: ")
result_sentence = []

# split into list
index = 0
for character in user_sentence:
    if index % 2 == 0:
        result_sentence.append(character.lower())
    else:
        result_sentence.append(character.upper())
    index += 1

result_string = "".join(result_sentence)
print(result_string)

Let's do some string manipulations!

Censorship... it's an awful thing, but money is money! And the banana empire is flush with cash.

Challenge: Implement censorship from the banana regime-- take space delimited sentence, if any word is apple, replace it with banana. If it's banana, replace it with "government-sponsored BANANA(TM)".

input_sentence = input("Give sentence: ")
input_split = input_sentence.split()

for word_index in range(len(input_split)):
    if "apple" in input_split[word_index].lower():
        input_split[word_index] = "banana"
    elif "banana" in input_split[word_index].lower():
        input_split[word_index] = "government-sponsored BANANA(TM)"

print(" ".join(input_split))

OK let's do practice exam questions

Spaced repetition is great, I plan to do some exam review for the next four sessions :)

Two sections of the midterm: Multiple choice (~40%) and free response (~60%). Our main topics thus far are:

Types of free response questions include:

Let's do exam prep!

Some extra multiple choice questions, just for fun...

When declaring a variable, what names are legal (in python, don’t have to follow coding standards)?

Answer: A, B

What variable name follows the coding standard for this class, and PEP8?

Answer: B

Consider the following code:

i = 0
L = [1, 2, 1, 5]
sum = 0
for i in L:
   sum += i + 3
print(sum)

What will it print out?

Answer: B

Consider the following code:

Answer: C

If you are given an integer (x), how can you write an if statement to test if it is even?

not (x or y) and z

Answer: B

Finally peace of mind 😌 Practice questions bring clarity to life...

Future practice will focus on other sections (free response: programming, short answer, and debugging).

I anticipate the programming free response to be the hardest. I'll have practice problems in future classes, but if you want to practice now, you can speedrun re-solve your homework, or check out the problems on codingbat (https://codingbat.com/python).