deepCopy是否复制从旧词典中删除后留下的空间？

Question

我正在尝试根据Python reclaiming memory after deleting items in a dictionary 从字典中删除键。后者提出的一个解决办法是：

to create a new dictionary by copying the old dictionary

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在源代码1中，我做了以下操作：

• 我创建了一个新词典new_flights
• 删除键del flights[key]
• 最后使用new_flights = copy.deepcopy(flights)

在源代码2中，我做了以下操作：

• 我创建了一个新词典new_flights
• 复制到新词典new_flights[key] = flights[key]
• 最后flights.clear()

两种方法都不起作用。内存没有被释放。你知道吗

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源代码1

 def remove_old_departure_dates(flights, search_date):
        new_flights = defaultdict(lambda : defaultdict(list))
        s_date = datetime.strptime(search_date,'%m/%d/%y')

        for key in flights.keys():
            dep_date = datetime.strptime(key.DDATE,'%m/%d/%y')
            if(s_date > dep_date):
                del flights[key]

        new_flights = copy.deepcopy(flights)
        flights.clear()
        return new_flights

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源代码2

def remove_old_departure_dates(flights, search_date):
    new_flights = defaultdict(lambda : defaultdict(list))
    s_date = datetime.strptime(search_date,'%m/%d/%y')

    for key in flights.keys():
        dep_date = datetime.strptime(key.DDATE,'%m/%d/%y')
        if(s_date > dep_date):
            new_flights[key] = flights[key]

    flights.clear()
    return new_flights

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讨论后的源代码

基于这些评论，我做了以下操作，并使用deepcopy删除了引用。好像起作用了。这是正确的吗？你知道吗

def remove_old_departure_dates(flights, search_date):
    old_flights = defaultdict(lambda : defaultdict(list))
    new_flights = defaultdict(lambda : defaultdict(list))
    s_date = datetime.strptime(search_date,'%m/%d/%y')

    for key in flights.keys():
        dep_date = datetime.strptime(key.DDATE,'%m/%d/%y')
        if(s_date > dep_date):
            print "removing dates " + key.DDATE +" "+search_date
            old_flights[key] = copy.deepcopy(flights[key])
        else:
            new_flights[key] = copy.deepcopy(flights[key])

    return (old_flights, new_flights)