Dictionary

###创建方式

a = dict()

a = {}

a = {'a': 1, 'b': 2}

a = dict(a=1,b=2)

a = [('a', 1), ('b', 2)]
b = dict(a)

a = zip('abc', [1,2,3])

a = { x:x*2 for x in range(10) }

a = dict.fromkeys(range(3), 'y')