python - Extending __str__() rather than replacing it

Question

I want to extend the __str__() method of my object. The str(obj) currently reads:

<mymodule.Test object at 0x2b1f5098f2d0>

I like the address as a unique identifier, but I want to add some attributes. What's the best way to extend this while still keeping the address portion? I'd like to look something like this:

<mymodule.Test object at 0x2b1f5098f2d: name=foo, isValid=true>

I dont' see any attribute that stores the address. I'm using python 2.4.3.

Edit: Would be nice to know how to do this with __repr__()

Solution (for python 2.4.3):

def __repr__(self):
    return "<%s.%s object at %s, name=%s, isValid=%s>" % (self.__module__,
           self.__class__.__name__, hex(id(self)), self.name, self.isValid)

Answer 1

You can get the address with id(obj). You probably want to change the __repr__() method instead of __str__(). Here's code that will do this in Python 2.6+:

class Test(object):
    def __repr__(self):
        repr_template = ("<{0.__class__.__module__}.{0.__class__.__name__}"
                         " object at {1}: name={0.name}, isValid={0.isValid}>")

        return repr_template.format(self, hex(id(self)))

Test with:

test = Test()
test.name = "foo"
test.isValid = True
print repr(test)
print str(test)
print test

You could easily do the same sort of thing in an older version of Python by using string formatting operations like "%s" instead of the clearer str.format() syntax. If you are going to use str.format(), you can also use its built-in hex formatting capability by using {1:#x} in the template and changing argument 1 from hex(id(self)) to simply id(self).

Answer 2

class Mine(object):
    def __str__(self):
        return object.__str__(self) + " own attributes..."