Thank you Alan, Dave and Cameron (and folks managing this email group)!
Your replies were very helpful.
Regards
ni
On Wed, Apr 9, 2014 at 4:25 AM, Cameron Simpson c...@zip.com.au wrote:
On 08Apr2014 22:58, Ni hung niih...@gmail.com wrote:
I am learning programming using python. I think of solving a problem
using
functions and for this reason all/most of my code consists of functions
and
no classes. I have some understanding of classes/Object Oriented
Programming. I can write simple classes but I do not understand when to
use
classes.
Loosely speaking, you can usefully make a class when there is a
particular type of object on which you are make an assortedment of
operations.
For example, if you have several functions looking like this:
def modify_thing1(obj1, ...):
def add_something(obj1, ...):
and so on, where obj1 is always the same kind of thing, representing
some well define idea you have when writing the code.
In that circumstance you might make a class looking like this:
class ObjName(object):
def __init__(self):
# self here is an obj1 as used above
# set whatever attributes an obj1 should have to start with
# you can pass in some of those values as parameters to the __init__
function
def modify(self, ...):
# this is the same as modify_thing1(obj1, ...) earlier
# using self as obj1
def add(self, ...):
# this is the same as add_something(obj1, ...) earlier
Then your code looks like:
obj1 = ObjName()
...
obj1.modify(5)
obj1.add(6)
or what have you.
This has several advantages:
- all the code that affects this kind of object is in one place
- you can remove all the specifics of how things are done from the main
code and keep them inside the class methods.
This makes the main code more readable (if you pick good method names)
and shorter (also more readable, usually).
- later, if need be, you can change the inner workings of how
ObjNames work without changing the main code, or at least not
much - sometimes not at all
Anyway, that's an ok rule of thumb for when to make a class: when
you have a bunch of operations to do to one type of thing.
Cheers,
--
Cameron Simpson c...@zip.com.au
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