On Thu, 23 Jun 2005 12:25:58 -0700, Paul McGuire wrote:
> But if you are subclassing str just so that you can easily print your
> objects, look at implementing the __str__ instance method on your
> class. Reserve inheritance for true "is-a" relationships. Often,
> inheritance is misapplied when the designer really means "has-a" or
> "is-implemented-using-a", and in these cases, the supposed superclass
> is better referenced using a member variable, and delegating to it.
Since we've just be talking about buzzwords in another thread, and the
difficulty self-taught folks have in knowing what they are, I don't
suppose somebody would like to give a simple, practical example of what
Paul means?
I'm going to take a punt here and guess. Instead of creating a sub-class
of str, Paul suggests you simply create a class:
class MyClass:
def __init__(self, value):
# value is expected to be a string
self.value = self.mangle(value)
def mangle(self, s):
# do work on s to make sure it looks the way you want it to look
return "*** " + s + " ***"
def __str__(self):
return self.value
(only with error checking etc for production code).
Then you use it like this:
py> myprintablestr = MyClass("Lovely Spam!")
py> print myprintablestr
*** Lovely Spam!!! ***
Am I close?
--
Steven
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