Question

如何在Python中将None对象转换为Decimal对象。

代码：

c['suspended_amount'] = sum([owned_license.charge_amount for owned_license in log.owned_licenses.all()])

错误：

TypeError: unsupported operand type(s) for +: 'decimal.Decimal' and 'NoneType'

Answer 1

跳过这些值：

c['suspended_amount'] = sum(owned_license.charge_amount
                            for owned_license in log.owned_licenses.all() 
                            if owned_license.charge_amount)

我删除了[..]方括号; sum()采用可迭代，我使用generator expression提供。使用方括号代替list comprehension，它将不必要地首先构建所有值的完整列表。 Sum只需要逐个获取值，它们不需要预先存在。

更好的是，要求数据库仅包含charge_amount不是NULL的那些行：

c['suspended_amount'] = sum(
    owned_license.charge_amount
    for owned_license in log.owned_licenses.exclude(charge_amount__isnull=True).all())

最好的，请让数据库为你做总结：

from django.db.models import Sum

c['suspended_amount'] = (
    log.owned_licenses.exclude(charge_amount__isnull=True)
        .aggregate(Sum('charge_amount'))['charge_amount__sum'])

请参阅Aggregation documentation。

Answer 2

您也可以使用＆＃39;或＆＃39;操作者：

c['suspended_amount'] = sum([owned_license.charge_amount or 0 for owned_license in log.owned_licenses.all()])

Python将无转换为十进制

2 个答案: