Lecture 10: October 31, 2019

Reading: §8
Due: Homework 3, due on November 8 at 11:59pm

  1. Dictionary
    1. Collection of key-value pairs
  2. Creating dictionaries
    1. Using d = { }
    2. Using d = dict()
  3. Methods for dictionaries
    1. k in D: True if dictionary D has key k; else False
    2. D.keys(): list of keys in D
    3. D.values(): list of values in D
    4. D.items(): list of tuples (key, value) in D
    5. D.get(k, d): if key k in D, return associated value; else return d
    6. del D[k]: delete tuple with key k from D
    7. D.clear(): delete all entries in D
  4. Example: memos
    1. Remember how slowly the recursive Fibonacci number program rfib.py ran? Here is a faster recursive version that uses memos [rfibmemo.py]
  5. Sorting the dictionary
    1. sorted sorts based on keys
  6. Example: word frequency count
    1. Unsorted [wfc-1.py]
    2. Sorted alphabetically [wfc-2.py]
    3. Sorted alphabetically, but dictionary order (note key=str.lower() in sorted [wfc-2a.py]
    4. Sorted by frequency (treat lambda x: x[1] as an idiom to reference the value of the dictionary entry, not the key—to go from highest to lowest, replace x[1] with -x[1]) [wfc-3.py]
    5. Sorted by frequency first, then alphabetically—note use of function alphafreq(x); you can use any function here, and the parameter is the item [wfc-4.py]

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Matt Bishop
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Version of October 30, 2019 at 7:30PM

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