针对今天关于初始值问题的记录

背景：对于for循环中第一个值 的问题，以及在减少遍历和不必要的功的情况下如何更新集合。

简要描述下类

class Coin(object):
    def __init__(self, introduction, worth)
        self.name = name
        self.worth = worth
        
class Gift(object):
    def __init__(self, discount, name, amount):
        self.discount = discount
        self.name = name
        self.amount = amount

class Wrapper(object):
    def __init__(self, coin, gift)
        self.coin = coin
        self.gift = gift
        
Test_Wrapper = Wrapper(
    coin=Coin('test', 10),
    gift = [Gift(20, 'A', 2), Gift(10, 'B', 3)])

第一次需求：

返回数据格式：{'coin':{'test': 10}, 'gift':{'A':2, 'B':3}}

实现方式：

class Wrapper(object):
    def __init__(self, coin, gift)
        self.coin = coin
        self.gift = gift
        
    @property
    def get_welfare_info(self):
        # 使用namedtuple
        WelfareInfo = namedtuple('WelfareInfo', 'coin gift')
        welfare_info = WelfareInfo(coin={}, gift={})
        if self.coin:
            welfare_info.coin[self.coin.name] = self.coin.worth
        if self.gift:
            for item in self.gift:
                # 此处合理利用字典的默认值属性，避免用if-else遍历处理
                welfare_info.gift.setdefault(item.name, 0)
                welfare_info.gitf[item.name] += item.amount
        return welfare_info

第二次需求：

返回数据格式：{'coin':[{'name': 'test', 'worth':10}],   
             'gift':[{'name': A, 'amount': 2}, {'name': B, 'worth': 3}]}

实现方式:
先来看下不合理的实现：

class Wrapper(object):
    def __init__(self, coin, gift)
        self.coin = coin
        self.gift = gift
        
    @property
    def get_welfare_info(self):
        # 使用namedtuple
        WelfareInfo = namedtuple('WelfareInfo', 'coin gift')
        welfare_info = WelfareInfo(coin=[], gift=[])
        if self.coin:
            coin_info = {'name': self.coin.name, 'worth': self.coin.worth}
            welfare_info.appned(coin_info)
        if self.gift:
            for item in self.gift:
                # 此处在大循环中嵌套小循环，做了很多无用功
                # 之后：name_list = set()              
                name_list = [item['name'] for item in welfare_info.gift]
                '''对列表做 in 操作的时间复杂度是 O(n)，  
                无论如何都不应该作为常规用法。判断 A 是否在   
                B 集合中，B 应该为哈希类型，Python 的哈希  
                类型包括字典 dict 和集合 set'''
                if item.name in name_list:
                    for c in welfare_info.gift:
                        if c['name'] == item.name:
                            c['worth'] += item.worth
                else:
                    gift = {'name': item['name'], 'worth':item['worth']}
                    welfare_info.gift.append(gift)
                    # 之后：name_list.add(item.name)
                return welfare_info

改进之后:

class Wrapper(object):
    def __init__(self, coin, gift)
        self.coin = coin
        self.gift = gift
        
    @property
    def get_welfare_info(self):
        # 使用namedtuple
        WelfareInfo = namedtuple('WelfareInfo', 'coin gift')
        welfare_info = WelfareInfo(coin_info=[], gift_info=[])
        Coin = namedtuple('Coin', 'info')
        Gift = namedtuple('Gift', 'info')
        if self.coin:
            coin = Coin(info={'name': self.coin.name, 'worth': self.coin.worth})
        if self.gift:
            gift_info = {}
            for item in self.gift:
                gift_info.setdefault(item.name, Gift(info={'name':item.name, 'amount':item.amount}))
                gift_info[item.name].info['amount'] += item.amount
            welfare_info.gift_info.extend(gift_info.values())
        return welfare_info