我得到了RuntimeError:在迭代期间字典更改了大小。Python

Here is my sample code:

这是我的示例代码:

def clean(record):

    record.pop('configurable_fields')
    record.pop('applied_discounts')
    record.pop('product_options')

    for key, value in record.items():
        if value is None:
            record.pop(key)

    return record
def clean