12.8. Exercises: Dictionaries

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  1. Part A

  2. Parts B and C

  3. Parts D and E

12.8.1. Part A: Search a Dictionary

The flavors dictionary contains entries that pair different ice cream flavors with their cost per scoop. Your job is to do the following:

  1. Write a function called return_cost that takes a dictionary and flavor choice as parameters.

    1. The function searches the dictionary for the flavor and returns its cost.

    2. If the flavor is not in the dictionary, return a value of 0.

  2. After coding the return_cost function, run the program and examine the output. Make sure your function behaves as expected before moving to the next step. Don’t forget to assign different strings to the choice variable!

  3. Write a function called fanciest_flavor that takes a dictionary as a parameter. The function should return the key name for the most expensive choice in the dictionary.

  4. Uncomment the 3 indicated lines in main(), then run the program several times and examine the output. Change the prices in flavors after each run to make sure your function correctly identifies the most expensive ice cream flavor.

Check your solutions.

12.8.2. Part B: Keys from a Collection

Use the accumulator pattern to add new key/value pairs to an empty dictionary.

  1. Write a function called assign_tickets that takes a list of names as a parameter.

  2. The function should take each name from the list and use it to create a key in the dictionary.

  3. For the value of each key, assign a random integer from 100-500.

    Tip

    We are not worried about giving two people the same ticket number in this exercise. However, for a real event we would want to prevent this.

    Check out the Unique Dictionary Values section in the Random Module appendix if you would like to avoid repeats in the values.

  4. Return the new dictionary.

  5. In main(), call the assign_tickets function and assign the result to a ticket_holders variable.

Print ticket_holders to check that your code works as expected. Your output should look something like:

{'Caleb': 192, 'Naomi': 490, 'Owen': 465, 'Ava': 248, 'Aaron': 421, 'Lydia': 306}

Check your solutions.

12.8.3. Part C: Modify Values

Oh no! Ticket numbers 100-199 were supposed to be held back for VIPs. You need to reassign tickets to anyone who was given one of the reserved seats. Use the editor in part B as you update your code.

Call the function fix_tickets, and use ticket_holders as the argument. The fix_tickets function should:

  1. Accept a dictionary as a parameter.

  2. Loop through the dictionary and check each ticket number to see if it is in the range 100-199 (including the end points).

  3. For a ticket within the range, increase its value by 500 and reassign it to the key.

  4. Unless you cloned the dictionary, there is no need to return the updated collection.

To check your code, be sure to print ticket_holders before and after calling the fix_tickets function.

Sample Output:

Before: {'Caleb': 168, 'Naomi': 205, 'Owen': 193, 'Ava': 161, 'Aaron': 246, 'Lydia': 330}
After: {'Caleb': 668, 'Naomi': 205, 'Owen': 693, 'Ava': 661, 'Aaron': 246, 'Lydia': 330}

Check your solutions.

12.8.4. Part D: Counting Characters

Write a function called character_count that counts how many times each character appears in a string.

The function should:

  1. Accept a string as a parameter.

  2. Create an empty dictionary called counts.

  3. Loop through the string and check each character.

    1. If the character does NOT exist in as a key in counts, add it and assign it a value of 1.

    2. If the character DOES exist as a key in counts, increase its value by one.

  4. Return the completed counts dictionary and assign it to a results variable in main().

The counting should be case-insensitive. For example, 'a' and 'A' both count as the same letter.

Be sure to print the returned dictionary to check your code.

Tip

Here are some test strings and their results:

  1. "Python ROCKS!" returns {'p': 1, 'y': 1, 't': 1, 'h': 1, 'o': 2, 'n': 1, ' ': 1, 'r': 1, 'c': 1, 'k': 1, 's': 1, '!': 1}.

  2. "Balloons, bookkeepers, and bubbles." returns {'b': 5, 'a': 2, 'l': 3, 'o': 4, 'n': 2, 's': 3, ',': 2, ' ': 3, 'k': 2, 'e': 4, 'p': 1, 'r': 1, 'd': 1, 'u': 1, '.': 1}.

Check your solutions.

12.8.5. Part E: Use a List to Sort Key/Value Output

Now display the character count result in a cleaner way. Update your code in the part D editor.

  1. In the main() function, loop through the results dictionary and print each key/value pair on its own line. For "B-A-L-L-O-O-N-S!", the output would be:

    The character counts for 'B-A-L-L-O-O-N-S!' are:
b: 1
-: 7
a: 1
l: 2
o: 2
n: 1
s: 1
!: 1

    Be sure your output includes the introductory sentence.

  2. Modify your code to print a key/value pair ONLY IF the character is a letter.

  3. Modify your code again, but this time display the character counts in alphabetical order.

    1. Use the list function to create a list of the keys from the results dictionary.

    2. Sort the list, then use a loop to print the key/value pairs, one pair per line.

The final output for "B-A-L-L-O-O-N-S!" should be:

The character counts for 'B-A-L-L-O-O-N-S!' are:
a: 1
b: 1
l: 2
n: 1
o: 2
s: 1

Check your solutions.