python - 使用 Jinja2 grouby 过滤器出现属性错误

Question

尝试让 groupby 过滤器正常工作时出现属性错误。我的 groupby 代码如下所示:

{% for year, year_purchases in purchases|groupby('PurchaseDate.year')|reverse %}
            <h2 class="year">{{ year }}</h2>
            {% for ... %}
            {% endfor %}
{% endfor %}

其中购买是PurchaseEntity的列表:

class PurchaseEntity:
    def __init__(self):
        self.PurchaseDate = ''
        self.Orders = []

    def load_from_query(self,result):
        self.PurchaseDate = result.PurchaseDate

我收到以下错误:

AttributeError
AttributeError: PurchaseEntity instance has no attribute '__getitem__'

问题似乎出在environment.py中:

def getitem(self, obj, argument):
"""Get an item or attribute of an object but prefer the item."""
try:
    return obj[argument]
except (TypeError, LookupError): #<-- Here it raises the error
    if isinstance(argument, basestring): #<-- It never reaches here
        try:
            attr = str(argument)
        except Exception:
            pass
        else:
            try:
                return getattr(obj, attr)
            except AttributeError:
                pass
    return self.undefined(obj=obj, name=argument)

我不认为这是 Jinja2 或“groupby”错误，因为 getitem 函数到处都在使用。我用谷歌搜索并找不到任何相关内容。但是，我所做的是更改“except (TypeError, LookupError):”行，并且它可以与任何此替代方案一起使用:

except:
except Exception:

我不知道我的类声明是否错误，或者我是否只是遗漏了一些东西，因为我尝试了其他类(由 SQLAlchemy 使用自动加载创建)并且工作正常。有什么建议吗？

顺便说一句，发送给 getitem 的参数是:

>>> (obj,argument)
(<project.logic.purchase.PurchaseEntity instance at 0x050DF148>, 'PurchaseDate')
>>> obj.PurchaseDate
datetime.datetime(2012, 9, 25, 17, 1, 44)

Answer 1

尝试使PurchaseEntity扩展对象:

class PurchaseEntity(object):

当您尝试查找某个项目但它们没有该项目时，不扩展任何内容的基本类会抛出 AttributeError 。对象抛出类型错误。

>>> class Foo:
...     def foo(self):
...             void    
... 
>>> class Bar(object):
...     def bar(self):
...             void
... 
>>> foo = Foo()
>>> bar = Bar()
>>> foo['foo']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: Foo instance has no attribute '__getitem__'
>>> bar['bar']
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'Bar' object has no attribute '__getitem__'