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  • for循环将字典添加到列表中出现覆盖前面数据的问题

    出现问题:

    rets = [{'id':1},{"id":2},{"id":3}]
    
    context = {}
    context['count'] = len(rets)
    req = []
    res = {}
    
    for ret in rets:
        res['a'] = ret['id']
        req.append(res)
    context['b'] = req
    print(context)

    如上述代码,想将rets中的数据通过for循环的方式添加到context里面想要得到如下类型的字典:

    {'count': 3, 'b': [{'a': 1}, {'a': 2}, {'a': 3}]}

    运行结果却是:

    {'count': 3, 'b': [{'a': 3}, {'a': 3}, {'a': 3}]}

    分析原因:

    rets = [{'id':1},{"id":2},{"id":3}]
    
    context = {}
    context['count'] = len(rets)
    req = []
    res = {}
    
    for ret in rets:
        print(ret)
        res['a'] = ret['id']
        req.append(res)
        print(req)
    context['b'] = req
    print(context)

    打印每次结果:

    {'id': 1}
    [{'a': 1}]
    {'id': 2}
    [{'a': 2}, {'a': 2}]
    {'id': 3}
    [{'a': 3}, {'a': 3}, {'a': 3}]
    {'count': 3, 'b': [{'a': 3}, {'a': 3}, {'a': 3}]}

    发现每次for循环之后添加到字典中,都会覆盖掉上次添加的数据.

    因为字典的增加方式dict1['aaa'] = bbb,这种形式是如果字典理由对应的key就会覆盖掉,没有对应的key就会添加到字典里。

    解决办法:

    rets = [{'id':1},{"id":2},{"id":3}]
    
    context = {}
    context['count'] = len(rets)
    req = []
    
    for ret in rets:
        res = {}
        print(ret)
        res['a'] = ret['id']
        req.append(res)
        print(req)
    context['b'] = req
    print(context)

    每次for循环都将字典初始化,然后再添加数据,就结觉问题了。

    打印结果:

    {'id': 1}
    [{'a': 1}]
    {'id': 2}
    [{'a': 1}, {'a': 2}]
    {'id': 3}
    [{'a': 1}, {'a': 2}, {'a': 3}]
    {'count': 3, 'b': [{'a': 1}, {'a': 2}, {'a': 3}]}

    结束!

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  • 原文地址:https://www.cnblogs.com/aaronthon/p/9729265.html
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