在for循环上将键添加到字典，获取runtimeerror

Question

我正在向字典中添加一个带有值的新键，但在运行代码时仍然会遇到运行时错误。我在同一次迭代中添加了两个单独的键。我可以让它在添加一个密钥时运行，但不能同时添加两个密钥。

向dict添加不起作用的条目的代码：

    for data in list:
        for value in data:
            if value == 'timestamp':
                timestamp = data[value]
                minute_shred = timestamp[14:16]
                second_shred = timestamp[17:19]
                    #change to x,y
                if minute_shred[0] == '0' and second_shred[0] == '0':
                    minute_shred = timestamp[15:16]
                    second_shred = timestamp[17:19]
                    data['minute'] = int(minute_shred)
                    data['second'] = int(minute_shred)
                    print(data['second'], timestamp)
                    #no change to x,y
                elif minute_shred[0] != '0' and second_shred[0] != '0':
                    data['minute'] = int(minute_shred)
                    data['second'] = int(minute_shred)
                    print(data['second'], timestamp)
                    # change to x, not y
                elif minute_shred[0] == '0' and second_shred[0] != '0':
                    minute_shred = timestamp[15:16]
                    data['minute'] = int(minute_shred)
                    data['second'] = int(second_shred)
                    print(data['second'], timestamp)
                    #change to y, not x
                elif minute_shred[0] != '0' and second_shred[0] == '0':
                    second_shred = timestamp[18:19]
                    data['second'] = int(second_shred)
                    data['minute'] = int(minute_shred)
                    print(data['second'], timestamp)

当在迭代中仅添加一个键时，此代码可以工作。

    for data in list:
        for value in data:
            if value == 'timestamp':
                timestamp = data[value]
                minute_shred = timestamp[14:16]
                if minute_shred[0] == '0':
                    minute_shred = timestamp[15:16]
                    data['minute'] = int(minute_shred)
                elif minute_shred[0] != '0':
                    data['minute'] = int(minute_shred)

我也尝试了一个接一个地添加它们，但没有成功，第二个for循环使用了添加数据的第二个逻辑，因为它产生了运行时错误。我确实注意到，如果在添加second_shred变量时将数据“‘second”更改为“data”adding，则可以正常工作。显然，我需要将它们添加为两个单独的键。

Answer 1

正如其他人所提到的，不要在迭代时修改迭代器。

如果您想迭代和修改数据，我强烈建议使用map或列表理解。

示例：

def modify(dict_val):
    # Code for modification as in your question

list = [map(modify, data) for data in list]

如果您不想将其用于将来的迭代，请确保在此为Python3的情况下将映射包装在list()中。

Answer 2

使用deepcopy工作。

    listcopy = copy.deepcopy(list)
    for item in listcopy:
        itemcopy = copy.deepcopy(item)
        for k in itemcopy:
            if k == 'timestamp':
                timestamp = item[k]
                second_shred = timestamp[17:19]
                if second_shred[0] == '0':
                    second_shred = timestamp[18:19]
                    item['second'] = int(minute_shred)
                elif second_shred[0] != '0':
                    item['second'] = int(minute_shred)