Lab 4e — Split and join

Review

10 minutes

Review this `cats_to_cougars.py” code from the guide on split and join:

def cats_to_cougars(line: str) -> str:
    words = line.split()
    new_words = []
    for word in words:
        if word == 'cat':
            word = 'cougar'
        new_words.append(word)
    return ' '.join(new_words)


def main():
    lines = ["BYU's mascot is cool, like a cat or something.",
             "Just like a cat can, he can catch stuff."]
    for line in lines:
        print(cats_to_cougars(line))


if __name__ == '__main__':
    main()

Discuss with the TA:

• How does cats_to_cougars() work? Be sure everyone understands every line of this code.
• What does split() do in this code?
• What does join() do in this code?
• What changes would we make to use replace()?
• Would using replace() change the functionality?
• Could we use string concatenation instead of a list?
• Note that split() is not needed to iterate for each character in a string, or for each string in a list. split() is used to convert a string into a list of tokens.

Cats and dogs

20 minutes

Write a program that:

• reads lines from input
• changes the lines so that
  • words containing ‘cat’ are surrounded with a cat emoji
  • words containing ‘dog’ are surrounded with a dog emoji
• prints out the new lines

You can find starter code in cats_and_dogs.py, which also has comments guiding you through the exerise.

When you run the finished program, you should see something like this:

python cats_and_dogs.py
> I like cats and dogs.
I like 🐈cats🐈 and 🐕dogs.🐕
> You should doggedly concatenate your strings!
You should 🐕doggedly🐕 🐈concatenate🐈 your strings!
> There is peace today -- dogs are sleeping with cats.
There is peace today -- 🐕dogs🐕 are sleeping with 🐈cats.🐈
>

This program has two pieces:

• The main() function handles the input loop. You should recognize this from Unit 3. Review the guide on input loops as needed.

• The do_subs() function takes the line and changes it as needed. This follows a new pattern, where you:

  • split() the line into a list of words
  • change some of the words
  • accumulate original and changed words in a new list
  • convert the list of words back into a string using join()

You can review the code and guide links above to see how to do this.

Discuss with the TA:

• How do you modify a word to have something before and after it?
• Share a solution and see if anyone did it differently.

Pet Population

20 minutes

Mike breeds pets and runs a pet store, but he hasn’t been receiving many customers lately. Out of curiosity, he wonders how his animal population will change over time if no one buys any pets.

Write a program to simulate a pet population over time. This program will take two arguments:

• the input file
• the output file

The input file looks like this, and shows how many animals there are:

animal,babies,juveniles,adults
bird,0,0,13
fish,19,0,0
rabbit,0,12,0
dog,7,3,2
cat,2,5,1

Notice how the first line is a header.

We have provided a main() function.

• First, it reads the lines of the input file.
• It calls the time_passes_for_store() once, which changes the lines as if one year had passed.
• It writes the new lines to the first output file.
• It calls the time_passes_for_store() function again, as if second year had passed.
• It writes the new lines to the second output file.

Follow these rules to change each line:

• If the first word in the column is animal, keep the whole line as it is.
• Babies become juveniles
• Juveniles become adults
• The new number of babies is equal to twice the previous number of adults.

For example if the line looks like this:

dog,3,4,7\n

You should change it to this:

dog,14,3,4\n

You can call the program like this:

python pet_population.py pets.txt year_one.txt year_two.txt

We have provided code in pet_population.py that decomposes the problem and has some comments to guide you. There are two main parts:

• time_passes_for_store should go through all the lines and call a function to do the doubling. It returns the new lines.

• change_pet_population takes just one line and does the modifications needed to swap the order and double the new babies quantities in that line.

Discuss with the TA:

• How do you split each line of a csv file?
• What are two different ways to access a specific item in a list?
• Share a solution and see if anyone did it differently.