Is it possible to subclass the immutable date class and override the __str__ method?

I am trying to subclass the immutable date class in Python, but I also need to override the __str__ method. So far, I have the following:

from datetime import date

class Year(date):
    def __new__(cls, year):
        return super(Year, cls).__new__(cls, year, 1, 1)
    def __str__(self):
        return self.st开发者_开发问答rftime('%Y')

Constructor works fine, but the __str__ method is completely ignored when I try to print the object. I have seen a few samples subclassing other immutable classes such as int and float. All of them were using the same convention. Am I missing something? Is there anything special for the date object?

UPDATE:

It seems that there is nothing wrong with the code. I was trying to print a Year object inside a Django template and since Django formats date objects using a localizable format __str__ method was being ignored.

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Add a return to the __str__ method.

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UPDATE:

I ran your updated code on my machine, and it works fine:

aj@localhost:~/so/python# cat date2.py
from datetime import date

class Year(date):
    def __new__(cls, year):
        return super(Year, cls).__new__(cls, year, 1, 1)
    def __str__(self):
        return self.strftime('%Y')

y=Year(2011)
print str(y)
aj@localhost:~/so/python# python date2.py
2011

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If this is your complete code you are missing the return statement:

def __str__(self):
    return self.strftime('%Y')