需求：['1:a','2:b','3:c'] 轉換為 {'1′: 'a','3′: 'c','2′: ''}

代碼如下:
a = {}
b = ['1:a','2:b','3:c']
map(lambda x:a.setdefault(x.split(':')[0], x.split(':')[1]), b)
print a
{'1': 'a', '3': 'c', '2': 'b'}