# 假如我们有一个字典,需要提取子集:
price = {
    "ACME": 45.23,
    "AAPL": 612.78,
    "IBM": 205.55,
    "HPQ": 37.2,
    "FB": 10.75
}

# 直接用字典推导式
p1 = {key :value for key, value in price.items() if value > 200}

# 提取key也是
keys = {"AAPL", "IBM", "HPQ", "MSFT"}
p2 = {key : value for key, value in price.items() if key in keys}

# 字典推导式是最快的方法,比下面两个办法都快:
dict((key, value) for key, value in price if value > 100)   # 快两倍
{key:price[key] for key in price.keys() if key in price.keys() & keys} # 快1.6倍