# Lecture 10: October 31, 2019

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]

 Matt Bishop Office: 2209 Watershed Sciences Phone: +1 (530) 752-8060 Email: mabishop@ucdavis.edu
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Version of October 30, 2019 at 7:30PM