1. import random

2. outcomes = {'heads':0, 'tails':0}

3. sides = outcomes.keys()

4. print(sides[0])

會產生錯誤：TypeError: 'dict_keys' object does not support indexing

這是由於python3改變了dict.keys,返回的是dict_keys物件,支援iterable 但不支援indexable，我們可以將其明確的轉化成list：

1. import random

2. outcomes = {'heads':0, 'tails':0}

3. sides = list(outcomes.keys())

4. print(sides[0]) # 輸出tails