Attribute error using Jinja2 grouby filter

问题

Trying to get the groupby filter to work I'm getting an Atribute error. My groupby code looks like:

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

Where purchases is a list of PurchaseEntity:

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

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

I'm getting the following error:

AttributeError
AttributeError: PurchaseEntity instance has no attribute '__getitem__'

The problem seems to be in environment.py:

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)

I don't think that its a Jinja2 or "groupby" error, because the getitem funcion is used everywhere. I googled it and couldn't fint anything related. However, what I did is change the "except (TypeError, LookupError):" line and It worked with any this alternatives:

except:
except Exception:

I don't know if my class delcaration is wrong or if I'm just missing something, because I tried with other clases (created by SQLAlchemy with autoload) and it worked fine. Any suggestions?

Btw, the arguments sent to getitem are:

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

回答1:

Try making PurchaseEntity extend object:

class PurchaseEntity(object):

Basic classes that do not extend anything throw an AttributeError when you try to lookup an item and they do not have it. Objects throw TypeError.

>>> 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__'

来源：https://stackoverflow.com/questions/12738338/attribute-error-using-jinja2-grouby-filter

标签

python

filter

group-by

jinja2