我收到RuntimeError：字典在迭代过程中更改了大小。 蟒蛇

Question

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

我收到此错误：

Traceback (most recent call last):
  File "C:\Users\Filipe\Dropbox\code\bigAnalysis\finalized scripts\importer.py", line 76, in <module>
    process_file('allOrderProductsData')
  File "C:\Users\Filipe\Dropbox\code\bigAnalysis\finalized scripts\importer.py", line 73, in process_file
    process_line(line)
  File "C:\Users\Filipe\Dropbox\code\bigAnalysis\finalized scripts\importer.py", line 58, in process_line
    product_id = dump_record('package', clean(package))  # id of recently created record
  File "C:\Users\Filipe\Dropbox\code\bigAnalysis\finalized scripts\importer.py", line 40, in clean
    for key, value in record.items():
RuntimeError: dictionary changed size during iteration

我尝试了在其他线程中找到的一些解决方案，例如使用copy.deecopy，但是到目前为止，它们都没有起作用。

Answer 1

采用

for key, value in list(record.items()):

代替

for key, value in record.items():

这样，您可以“冻结”要迭代的项目列表。 record.items()是仍然保留对原始字典的引用的生成器。 list(record.items())是一个独立的列表。

Answer 2

为了避免在迭代过程中更改字典大小，可以改为返回一个新的字典：

def clean(record):

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

    return {k: v for k, v in record.items() if v is not None}