[Tutor] OO re-factoring (was Pythonese/Efficiency/Generalese critique)

[Lee Cullens]

Thanks again for your thoughts Javier.

You've certainly given me a mouthful to chew on :~)  I was thinking  
more in terms of "OOP is about code reuse" and trying to equate the  
function approach to such with the class methods approach in a  
similar way.  Obviously I have got my mind wrapped around the wrong  
tree.


I'm not actually looking for the best approach here - rather just  
trying to map a concept I'm familiar with to a new (to me) concept.   
The idea being than one learns from doing :')  My initial thought  
that it would be a simple reusable code structure to re-map is  
shaping up otherwise.

Thanks,
Lee C


On Jun 8, 2005, at 1:10 AM, Javier Ruere wrote:


> Lee Cullens wrote:
>
>
>> I was thinking of extending the learning exercise by re-factoring it
>> as an OO approach, since it would contain a minimum altered method.
>> Being new to OOP also though, I'm confusing myself with how that
>> would be best accomplished.  My thinking is that class/subclass
>> method instances would replace the recursive functions approach, but
>> have as yet not formed the coding in my mind.
>>
>>
>
>    I can't imagine this either and, though I'm no OO guru, have never
> considered that that an inheritance relationship could replace a
> recursive function call.
>
>
>
>> I've read a lot on OOP, but seem to have a problem with the practical
>> use of such in this utility.  I'm undoubtedly creating a mountain of
>> an ant hill in my mind, so any thoughts would be appreciated.
>>
>>
>
>    I don't see any benefit from using OO in this case. Module level
> functions (like you have now) are ideal in this case IMHO.
>    Maybe in a situation where you can benefit from OO it would be
> crearer how to use it. Having state is usually a good sign. Working  
> with
> several "things" which have a behaviour would be another.
>    Just for fun lets do it anyway. :) Directories and files could be
> considered things, files could tell if they are files, links or  
> whatever
> and directories could tell which subdirectories and files they have.
> Also this objects could render themselfs to a proper string
> representation we can directly output as a row.
>    So, in pseudocode, this would be something like:
>
> class File:
>    """File(name:str, parent:Dir)
>
>    parent: The directory which contains this File.
>    name: The name of this File.
>    """
>    def __init__(self, name, parent):
>      self._parent = parent
>      self._name = name
>
>      assert exists(join(repr(parent), name))
>
>    def isLink(self):
>      return islink(self.path)
>
>    [Rest of the is* functions.]
>
>    def __str__(self):
>      return [...]
>
> class Dir:
>    """Dir(name:str, [parent:Dir])
>
>    parent: The directory which contains this File.
>            If omited, an absolute path is assumed.
>    name: The name of this File.
>    """
>    def __init__(self, name, parent=None)
>      self._parent = parent
>      self._name = name
>
>      assert isdir(join(repr(parent), name))
>
>    def getDirs(self):
>      return [...]
>
>    def getFiles(self):
>      return [...]
>
>    Now, both classes could inherit from a FSElement (or something)  
> but I
> see no benefit in doing that.
>    The output functionality could also be in a different class:
>
> class CSVOutput:
>    def __init__(self, filename):
>      [validate for overwritting]
>      self._out = file(filename, 'w')
>
>    def process(self, root):
>      for file in root.getFiles():
>        self._out.write(str(file))
>
>      for dir in root.getDirs():
>        self.process(dir)
>
>    And the main:
>
> CVSOuput(argv[2]).process(Dir(mkAbsolutePath(argv[1])))
>
>    I'm very sleepy so this could all just be gibberish but I hope it
> will help you get the idea. Ideally, functions should be very small, a
> couple of lines, and object should be reusable. So moving the  
> rendering
> to CVSOutput would be better. :)
>
> Javier
>
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