Tricks with Dictionaries in Python

Python-Dict-tricks.py

# Categorizing to dicts
words = ['apple', 'bat', 'bar', 'atom', 'book']
by_letters = {}

for word in words:
    letter = word[0]
    by_letters[letter] = by_letters.get(letter, 0) + 1
    value = by_letters[letter]
    print('Letter: {} - Count: {}'.format(letter, value))

by_letters = {}
for word in words:
    letter = word[0]
    by_letters.setdefault(letter, []).append(word)
print(by_letters)

# Empty Dict that ready-to-set default values
from collections import defaultdict
by_letters = defaultdict(list)
for word in words:
    by_letters[word[0]].append(word)
    print(by_letters)