Dictionary Exercises

Dictionaries will be very useful in the various text problems that we will address. Today's exercises are a mixture of some dictionary basics, plus a couple exercises that serve as a foundation for upcoming bigger exercises.

As always, collaborate with your neighbor and upload your solutions. If you finish early, you can work on your current assignment.

Dictionary basics

• What does the following do? Try to figure it out yourself before using CodeSkulptor.

  ingredients = {}
  ingredients["bread"] = "1 slice"
  ingredients["peanut butter"] = "1 ounce"
  ingredients["jelly"] = "1 ounce"
  ingredients["bread"] = "2 slices"
  
  print ingredients
  

• For this set of exercises, we want to use dictionaries that map numbers to numbers. In other words, both the keys and the values are numbers.

  • Define such a dictionary.

  • How can you add up all of the numbers that are keys? Hint: What is the easiest way to get a list of all the keys?

  • How can you add up all of the numbers that are values? Hint: What is the easiest way to get a list of all the values?

• What is wrong with the following dictionary definition?

  d = {10 : 4, "good" : "buddy", ["This example"] : ("is", "silly"), ("So", "is") : ["this", "one"]}
  

More Dictionary Examples

• Define a function dict_squares_range(start, stop, step). It returns a dictionary such that for each number in range(start, stop, step), the dictionary maps that number to its square.

  For example, dict_squares_range(3, 8, 2) should return {3 : 9, 5 : 25, 7 : 49}.

  Test your dict_squares_range function using OwlTest

• Assume you have a dictionary that maps numbers to numbers, as in the previous two exercises. Use simpleplot.plot_lines() to plot the points that this dictionary represents.

  Read the CodeSkulptor documentation for simpleplot.plot_lines(). Note that it allows you to use a dictionary to represent a data set.

• Define a function print_mapping() that takes a dictionary. It prints each key/value pair, one per line.

  For example, print_mapping({3 : 9, 5 : 25, 7 : 49}) should print the following lines in some order.

  3 maps to 9
  5 maps to 25
  7 maps to 49