"Paul Boddie" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
<snip>
> Moreover, append and insert return
> no result because the change occurs within an existing object - if you
> were to return a reference to the changed object, it would be the same
> reference as the one you already had.
>
There's nothing wrong with returning self from a mutator. This was a common
idiom in Smalltalk (the syntax for this was "^self", which was probably the
most common statement in any Smalltalk program), and permitted the chaining
of property mutators into a single line, each invoking a mutator and
returning self, which was then used to invoke the next mutator, etc. For
instance, you could have a class like this:
class Box(object):
def __init__(self):
self.ln = 0
self.wd = 0
self.ht = 0
def length(self,ln):
self.ln = ln
return self
def width(self,w):
self.wd = w
return self
def height(self,h):
self.ht = h
return self
volume = property(lambda self:self.ln*self.wd*self.ht)
bx = Box().length(100).width(50).height(20)
print bx.volume
I guess this is sort of a trivial example, and in its triviality, even
borders on un-Pythonic. But it is useful when you want to support a large
set of object attributes, without creating an init method with many, many
args. Even in this case, an init method that takes length, width and height
args must always get them specified in the correct order, or use named args.
But with mutators that return self, a client could write any of these:
bx = Box().length(100).width(50).height(20)
bx = Box().width(50).height(20).length(100)
bx = Box().width(50).length(100).height(20)
...etc...
and the results are the same.
-- Paul
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