A dictionary stores associations between data by mapping each key to a value. For example, a word-frequency dictionary maps each word to the number of times it appears. Keys must be unique, but values may repeat. section 5.1.3
Use dictionaries to store and work with changing associated data:
- Access a value with index notation, such as freq['DNA']. Key matching is case-sensitive, so freq['dna'] raises a KeyError when only DNA exists. section 5.1.3
- Change an existing value with indexing, as in freq['morph'] = 6. section 5.1.3
- Use methods such as keys(), values(), and pop(), and loop through keys to process every associated value. section 5.1.3
Scrabble letter scores
A points dictionary can map each letter to its score, such as {'a': 1, 'b': 3, 'z': 10}. A scoring function then looks up points[char] for every character and sums the results. For example, num_points('zap') returns 14. section 3.3.4
>>> freq
{'DNA': 11, 'acquire': 11, 'Taxxon': 13, 'Controller': 20, 'morph': 41}
>>> freq.keys() #1
dict_keys(['DNA', 'acquire', 'Taxxon', 'Controller', 'morph'])
>>> freq.values() #2
dict_values([11, 11, 13, 20, 41])
>>> freq.pop('Controller') #3
20
>>> freq
{'DNA': 11, 'acquire': 11, 'Taxxon': 13, 'morph': 41}
Inspect dictionary contents, retrieve keys and values, remove an entry, and observe the changed mapping. section 5.1.3
