Topic: Dictionaries
Related Reading: Chapter 23
Due: 10:00am, Tuesday, 27 November 2018

Please make sure you adhere to the policies on academic integrity.

1. (5 points)

   Assume that the method dict.items() did not exist. Give a small code fragment that produces a list of (key,value) pairs for a dictionary named data.

2. (5 points)

   Although not discussed in the chapter, Python dictonaries also support a method named setdefault, documented as follows:

   	setdefault(key, default)
   	  if key is in the dicitonary, return its value. If
   	  not, insert key with a value of default and
   	  return default.

   Demonstrate your understanding by giving a snippet of code with logic that is equivalent to the following:

   val = capital.setdefault('CA','Springfield')
   

   presuming that capital is an existing dictionary. You are not allowed to use the setdefault method in your answer.

3. (10 points)

   Write a function with signature letterFrequency(word) that returns a dictionary that maps each occurrying letter of the string word to a count of the number of times that letter occurs. For example, letterFrequency('Mississippi') should return a dictionary with entries {'M':1, 'i':4, 's':4, 'p':2}

   With proper use of dictionaries, your function should require only a single loop through the characters of the string, updating the frequency counts as you proceed. You should avoid use of the str.count method (which itself would depend on a loop).