pass object or use self.object?

[Lie Ryan]

On 04/06/10 23:52, Tim Arnold wrote:
> Hi,
> I have a few classes that manipulate documents. One is really a
> process that I use a class for just to bundle a bunch of functions
> together (and to keep my call signatures the same for each of my
> manipulator classes).
> 
> So my question is whether it's bad practice to set things up so each
> method operates on self.document or should I pass document around from
> one function to the next?
> pseudo code:
> 
> class ManipulatorA(object):
>     def process(self, document):
>         document = self.do_one_thing(document)
>         document = self.do_another_thing(document)
>         # bunch of similar lines
>         return document
> 
> or
> 
> class ManipulatorA(object):
>     def process(self, document):
>         self.document = document
>         self.do_one_thing() # operates on self.document
>         self.do_another_thing()
>         # bunch of similar lines
>         return self.document

Since in function in python is a first-class object, you can instead do
something like:

def process(document):
    # note: document should encapsulate its own logic
    document.do_one_thing()
    document.do_another_thing()

And when you need some complex logic, you can easily elevate your
function to a class:

class Appender(object):
    def __init__(self, text):
        self.text = text
    def __call__(self, document):
        mtext = self.manipulate(document, text)
        document.append(mtext)

and I think for your purpose, the mixin pattern could cleanly separate
manipulation and document while still obeying object-oriented pattern
that document is self-sufficient:

# language with only single-inheritance can only dream to do this
class Appendable(object):
    def append(self, text):
        self.text += text
class Savable(object):
    def save(self, fileobj):
        fileobj.write(self.text)
class Openable(object):
    def open(self, fileobj):
        self.text = fileobj.read()
class Document(Appendable, Savable, Openable):
    def __init__(self):
        self.text = ''