Chapter 12: Python Dictionaries

The answers on this page show ONE way to solve the exercises. However, there are usually OTHER ways to accomplish the same thing. This is OK!

A suggested solution is ONE way to solve the problem, not the ONLY way.

Chapter Sandbox

Use the editor below to test out any of the solutions!

Solutions

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.

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    def return_cost(menu, item):
   if item in menu:        # Check if 'item' is a key in the 'menu' dictionary.
      return menu[item]   # Return the value for the key.
   return 0                # If 'item' isn't in the dictionary, return 0.

  1. 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.

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    # Write your fanciest_flavor function here:
def fanciest_flavor(menu):  # 'menu' is the dictionary sent to the function.
   highest_cost = 0
   fanciest = ''
   # Loop through each key/value pair in the dictionary.
   for (flavor, price) in menu.items():
      if price > highest_cost:    # Compare the price for the current flavor vs. highest_cost.
            fanciest = flavor       # If True, reassign the most expensive flavor
            highest_cost = price    # and the highest_cost.
   return fanciest

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Part B: Keys from a Collection

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

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

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

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    tickets = {}        # Create an empty dictionary.
for name in names:  # Loop through the 'names' list.
tickets[name] = random.randint(100, 500)    # Assign a random number from 100 - 500 to the 'name' key.

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

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    def main():
   names = ['Caleb', 'Naomi', 'Owen', 'Ava', 'Aaron', 'Lydia']

   ticket_holders = assign_tickets(names)
   print(ticket_holders)

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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.

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.

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    def fix_tickets(tickets):
# Iterate through the key/value pairs in the dictionary:
for (key, value) in tickets.items():
  if 100 <= value <= 199:     # Check if 'value' is in the desired range.
      tickets[key] += 500     # If True, increase 'value' by 500 and reassign it to the key.

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

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    # In main:
print('Before:', ticket_holders)
fix_tickets(ticket_holders)
print('After:', ticket_holders)

Back to exercises.

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. Create an empty dictionary called counts.

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    counts = {}                     # Define an empty dictionary.

  2. 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.

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

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    for char in a_string.lower():   # Loop through each character in a_string.

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

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    #In the main function under the variable text
# Call the character_count() function. Assign the returned dictionary to results.

results = character_count(text)

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

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    # Print the introductory sentence:
print("The letter counts for '{0}' are:".format(text))

# Loop through the dictionary:
for (key, value) in results.items():
   # Check if key is a letter.
   if key in string.ascii_letters:
      # If True, print the key and its value from the results dictionary.
      print(f"{key}: {value}")

  2. 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.

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    # Create a list of the keys from the results dictionary.
keys = list(results.keys())

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

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    # Sort the keys alphabetically.
keys.sort()

for key in keys:
   # Check if key is a letter.
   if key in string.ascii_letters:
      # If True, print the key and its value from the results dictionary.
      print('{0}: {1}'.format(key, results[key]))

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